Trigonometry : Trigonometry

Study concepts, example questions & explanations for Trigonometry

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Example Questions

Example Question #611 : Trigonometry

Find the difference of the two vectors, \(\displaystyle \vec{A}\) which ends at \(\displaystyle (-2, 4)\)  and \(\displaystyle \vec{B}\) ending at \(\displaystyle (7, -6)\).

 

 

Possible Answers:

-

\(\displaystyle (-9, 10)\)

-

-

Correct answer:

\(\displaystyle (-9, 10)\)

Explanation:

When finding the difference of two vectors, you must subtract the x and y components separately.

\(\displaystyle \vec{A} - \vec{B} = (-2, 4) - (7, -6)\)

\(\displaystyle \vec{A} - \vec{B} = (-2-7, 4 - (-6))\)

\(\displaystyle \vec{A} - \vec{B} = (-9, 10)\)

Example Question #6 : Vectors

Which of the following is the correct depiction of the difference of vectors A and B?

Screen shot 2020 08 27 at 1.42.05 pm

Possible Answers:

Screen shot 2020 08 27 at 1.43.50 pm

Screen shot 2020 08 27 at 1.43.37 pm

Screen shot 2020 08 27 at 1.43.01 pm

Screen shot 2020 08 27 at 1.43.44 pm

Correct answer:

Screen shot 2020 08 27 at 1.43.01 pm

Explanation:

To find the difference of two vectors we must consider the x and y components separately.

\(\displaystyle \vec{A} - \vec{B} = (5, 8) - (-3, 10)\)

\(\displaystyle \vec{A} - \vec{B} = (5 - (-3), 8 - 10)\)

\(\displaystyle \vec{A} = \vec{B} = (8, -2)\) 

And then we must correctly graph this vector

Screen shot 2020 08 27 at 1.43.01 pm

Example Question #2 : Vectors

True or False: The magnitude of a vector is the length of the vector.

Possible Answers:

True 

False

Correct answer:

True 

Explanation:

When finding the magnitude of the vector, you use either the Pythagorean Theorem by forming a right triangle with the vector in question or you can use the distance formula.  This is much more clear considering the distance vector that the magnitude of the vector is in fact the length of the vector.

Example Question #1 : Bearing

Which of the following could represent an aeronautical bearing of \(\displaystyle 215^\circ\)?

Possible Answers:


Screen shot 2020 08 03 at 1.15.33 pm

Screen shot 2020 08 03 at 1.11.51 pm

Screen shot 2020 08 03 at 12.59.14 pm

Screen shot 2020 08 03 at 1.00.54 pm

Screen shot 2020 08 03 at 1.00.35 pm

Correct answer:

Screen shot 2020 08 03 at 1.00.35 pm

Explanation:

The correct image depicting an aeronautical bearing of \(\displaystyle 215^\circ\) is 

Screen shot 2020 08 03 at 1.00.35 pm

This image begins at north, and moves \(\displaystyle 215^\circ\) clockwise from it. 

Three of the given incorrect answers depict \(\displaystyle \textup S35^\circ\textup W\)\(\displaystyle 145^\circ\)\(\displaystyle 325^\circ\). The fourth incorrect answer does not represent a standard bearing convention as it is neither an acute angle, nor in the clockwise direction. That incorrect answer looks like:

Screen shot 2020 08 03 at 1.11.51 pm

Example Question #1 : Bearing

Which of the following diagrams could show a bearing of \(\displaystyle \textup S35^\circ\textup W\)?

 

Possible Answers:

Screen shot 2020 08 03 at 1.15.33 pm

Screen shot 2020 08 03 at 1.11.14 pm

Screen shot 2020 08 03 at 1.14.52 pm

Screen shot 2020 08 03 at 12.58.23 pm

Correct answer:

Screen shot 2020 08 03 at 1.15.33 pm

Explanation:

The bearing of a point B from a point A in a horizontal plane is defined as the acute angle made by the ray drawn from A through B with the north-south line through A. The bearing is read from the north or south line toward the east or west. Bearing is typically only represented in degrees (or degrees and minutes) rather than radians. To find \(\displaystyle \textup S35^\circ\textup W\), start in the south direction, then move \(\displaystyle 35^\circ\) towards the west:

Screen shot 2020 08 03 at 1.15.33 pm

 

 

The other incorrect answer choices provided depict \(\displaystyle \textup S 35^\circ \textup E\)\(\displaystyle \textup N 35^\circ \textup E\), and \(\displaystyle \textup N 35^\circ \textup W\).

Example Question #11 : Practical Applications

The following diagram could represent which one of these practical scenarios?

Screen shot 2020 08 03 at 1.42.02 pm

Possible Answers:

A race car traveling \(\displaystyle \textup S 30^\circ \textup E\) at \(\displaystyle 180\) miles per hour

A motorboat traveling \(\displaystyle \textup S 30^\circ \textup W\) at \(\displaystyle 60\) miles per hour for \(\displaystyle 3\) hours

A helicopter traveling \(\displaystyle \textup S 30^\circ \textup W\) at \(\displaystyle 50\) miles per hour for \(\displaystyle 3\) hours

An airplane traveling \(\displaystyle \textup N 30^\circ \textup E\) at \(\displaystyle 180\) miles per hour

Correct answer:

A motorboat traveling \(\displaystyle \textup S 30^\circ \textup W\) at \(\displaystyle 60\) miles per hour for \(\displaystyle 3\) hours

Explanation:

This question and its answer choices give you a few clues to work with. First, we need to identify the bearing angle being shown. The options in the answer choices are either \(\displaystyle \textup N 30^\circ \textup E\)\(\displaystyle \textup S 30^\circ \textup W\), or \(\displaystyle \textup S 30^\circ \textup E\). Because the angle begins in the south direction and moves \(\displaystyle 30^\circ\) towards the west, the correct bearing is \(\displaystyle \textup S 30^\circ \textup W\). That means only two of the answer choices could be correct. We now need to understand how the \(\displaystyle 180\) miles per hour corresponds to the problem. Notice that there is no answer choice that has the bearing of \(\displaystyle \textup S 30^\circ \textup W\) and velocity of \(\displaystyle 180\) miles per hour. Rather, we need to choose between \(\displaystyle 60\) miles per hour for \(\displaystyle 3\) hours or \(\displaystyle 50\) miles per hour for \(\displaystyle 3\) hours. Because \(\displaystyle 60\) miles per hour for \(\displaystyle 3\) hours corresponds to \(\displaystyle 180\) (whereas the other option corresponds to only \(\displaystyle 150\)), the correct answer is "A motorboat traveling \(\displaystyle \textup S 30^\circ \textup W\) at \(\displaystyle 60\) miles per hour for \(\displaystyle 3\) hours."

Example Question #12 : Practical Applications

A ship moves in the direction \(\displaystyle \textup S 30^\circ \textup E\) at a speed of \(\displaystyle 35\) miles per hour for \(\displaystyle 6\) hours. How far south and how far east is the ship from its starting position?

Possible Answers:

181.87 miles south and 105 miles east

17.5 miles south and 30.31 miles east

30.31 miles south and 17.5 miles east

105 miles south and 181.87 miles east

Correct answer:

181.87 miles south and 105 miles east

Explanation:

First, let's set up a diagram using the given information. This looks like this:

Screen shot 2020 08 03 at 2.07.54 pm 

Next, let's convert this info into a triangle so that we can use trigonometry to solve the problem. We need to calculate that the ship going \(\displaystyle 35\) miles per hour for \(\displaystyle 6\) hours will have traveled \(\displaystyle 35\cdot 6=210\) miles. 

Screen shot 2020 08 03 at 2.12.15 pm

Now we can use trigonometry to determine the missing sides, s and e.

\(\displaystyle \cos 30^\circ=\frac{s}{210}\)

\(\displaystyle 210\cos 30^\circ=s\)

\(\displaystyle 210\cdot \frac{\sqrt3}{2}=181.87=s\)

\(\displaystyle \sin 30^\circ=\frac{e}{210}\)

\(\displaystyle 210\sin 30^\circ=e\)

\(\displaystyle 210\cdot \frac{1}{2}=105=e\)

Therefore the ship has travelled 181.87 miles south and 105 miles east. 

Example Question #2 : Bearing

An airplane is traveling at a bearing of \(\displaystyle 115^\circ\) from north for 330 kilometers. How far south and how far east is the plane from its starting point?

Possible Answers:

The airplane is 299.08 km south of its starting point and 139.46 km east of its starting point.

The airplane is 139.46 km south of its starting point and 707.69 km east of its starting point.

The airplane is 139.46 km south of its starting point and 299.08 km east of its starting point.

The airplane is 707.69 km south of its starting point and 139.46 km east of its starting point.

Correct answer:

The airplane is 139.46 km south of its starting point and 299.08 km east of its starting point.

Explanation:

First, let's incorporate the given information into a diagram. Start by labelling the plane's bearing of \(\displaystyle 115^\circ\) along with its velocity 330km. Next, draw a line segment to complete the triangle and determine the measures of the angles of the triangle. We can determine the angle \(\displaystyle 65^\circ=180^\circ-115^\circ\), we constructed the diagram such that there is a right angle, and finally we can find the third angle by taking \(\displaystyle 180^\circ-65^\circ-90^\circ=25^\circ\)

Screen shot 2020 08 03 at 2.38.56 pm

The question is asking us how far south and how far east the plane is from its starting point, so we need to now use trigonometry to determine the lengths of the missing sides of the triangle. We will call these sides s for the southward distance and e for the eastward distance.

\(\displaystyle \cos65^\circ=\frac{s}{330}\)

\(\displaystyle 330\cos65^\circ=s\)

\(\displaystyle s=139.46\) km

\(\displaystyle \sin65^\circ=\frac{e}{330}\)

\(\displaystyle 330\sin65^\circ=e\)

\(\displaystyle e=299.08\) km

Therefore the airplane is 139.46 km south of its starting point and 299.08 km east of its starting point.

Example Question #3 : Bearing

Three ships are positioned in the following way: Ship A is 240 miles due west of Ship C, and Ship B is due south of Ship C. Ship B bears \(\displaystyle \textup S22^\circ\textup E\) from Ship A. How far is Ship B from Ship A? How far is Ship B from Ship C? What is the bearing from Ship A to Ship B?

Possible Answers:

Distance from Ship A to Ship B: 640.67 miles

Distance from Ship B to Ship C: 594.02 miles

Bearing from Ship B to Ship A: \(\displaystyle \textup N22^\circ\textup W\)

Distance from Ship A to Ship B: 594.02 miles

Distance from Ship B to Ship C: 640.67 miles

Bearing from Ship B to Ship A: \(\displaystyle \textup S22^\circ\textup E\)

Distance from Ship A to Ship B: 594.02 miles

Distance from Ship B to Ship C: 640.67 miles

Bearing from Ship B to Ship A: \(\displaystyle \textup N22^\circ\textup W\)

Distance from Ship A to Ship B: 640.67 miles

Distance from Ship B to Ship C: 594.02 miles

Bearing from Ship B to Ship A: \(\displaystyle \textup S22^\circ\textup E\)

Correct answer:

Distance from Ship A to Ship B: 640.67 miles

Distance from Ship B to Ship C: 594.02 miles

Bearing from Ship B to Ship A: \(\displaystyle \textup N22^\circ\textup W\)

Explanation:

To solve this problem, begin with a diagram, and label all known information. We know that we can label two angles as \(\displaystyle 22^\circ\) and one length as 240. Then, by deductive reasoning, we can label another angle as \(\displaystyle 68^\circ\) because \(\displaystyle 90^\circ-22^\circ=68^\circ\).

Screen shot 2020 08 03 at 3.33.07 pm

Next, we need to use trigonometry to find the answers to each question we're being asked. To find the distance AB, set up

\(\displaystyle \cos68^\circ=\frac{240}{AB}\)

\(\displaystyle AB=\frac{240}{\cos68^\circ}\)

\(\displaystyle AB=640.67\)

Next, we can find the distance BC. There are two ways to do this since we know two angles of the triangle, but either way you need to use the tangent function.

\(\displaystyle \tan68^\circ=\frac{BC}{240}\)

\(\displaystyle 240\tan68^\circ=BC\)

\(\displaystyle 594.02=BC\)

Finally, we are asked to find the bearing from Ship B to A. Be careful, because in the initial problem we are given the Bearing from Ship A to Ship B. While the angle will remain the same, the direction is different because we are starting at a different initial point (B instead of A). With B as your starting point, A is north and west. Therefore the bearing from Ship B to Ship A is \(\displaystyle \textup N22^\circ\textup W\).

 

Therefore the correct distance between Ships A and B is 640.67 miles, the distance between ships B and C is 594.02 miles, and the bearing from Ship B to Ship A is  \(\displaystyle \textup N22^\circ\textup W\).

Example Question #4 : Bearing

Three cruise ships are situated as follows: Sea Terraformer is 200 miles due north of Wave Catcher, and Island Pioneer is 345 miles due east of Wave Catcher. What is the bearing from Island Pioneer to Sea Terraformer, and what is the bearing from Sea Terraformer to Island Pioneer?

Possible Answers:

Bearing from Island Pioneer to Sea Terraformer: \(\displaystyle \textup S59.9^\circ\textup E\)

Bearing from Sea Terraformer to Island Pioneer: \(\displaystyle \textup N 30.1^\circ \textup W\)

Bearing from Island Pioneer to Sea Terraformer: \(\displaystyle \textup N59.9^\circ\textup W\)

Bearing from Sea Terraformer to Island Pioneer: \(\displaystyle \textup S59.9^\circ\textup E\)

Bearing from Island Pioneer to Sea Terraformer: \(\displaystyle \textup N 30.1^\circ \textup W\)

Bearing from Sea Terraformer to Island Pioneer: \(\displaystyle \textup S59.9^\circ\textup E\)

Bearing from Island Pioneer to Sea Terraformer: \(\displaystyle \textup S59.9^\circ\textup E\)

Bearing from Sea Terraformer to Island Pioneer: \(\displaystyle \textup N59.9^\circ\textup W\)

Correct answer:

Bearing from Island Pioneer to Sea Terraformer: \(\displaystyle \textup N59.9^\circ\textup W\)

Bearing from Sea Terraformer to Island Pioneer: \(\displaystyle \textup S59.9^\circ\textup E\)

Explanation:

Begin by diagramming the given information; you'll see that the three ships create a right triangle. To solve the question, we need to find the unknown angles of the triangle, then frame our answers as the proper bearings. 

Screen shot 2020 08 03 at 3.11.36 pm

First let's solve for the topmost angle in the diagram, which we'll call \(\displaystyle \angle S\).

\(\displaystyle \tan S=\frac{345}{200}\)

\(\displaystyle \tan^-^1\left ( \frac{345}{200} \right )=59.9^\circ=\angle S\)

By alternate interior angles, the other diagrammed angle will also be equal to \(\displaystyle 59.9^\circ\).

Now, put your cursor on Island Pioneer, and see if you need to move north or south, and then east or west to get to Sea Terraformer. You need to move north, then west. Therefore the bearing between Island Pioneer and Sea Terraformer is \(\displaystyle \textup N59.9^\circ\textup W\). Now put your cursor on Sea Terraformer and complete the same process to get to Island Pioneer; you'll go south, then east. Therefore the bearing from Sea Terraformer to Island Pioneer is \(\displaystyle \textup S59.9^\circ\textup E\).

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