High School Math : Geometry

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #2 : How To Find An Angle In An Acute / Obtuse Triangle

 

 

Let the measures, in degrees, of the three angles of a triangle be x, y, and z. If y = 2z, and z = 0.5x - 30, then what is the measure, in degrees, of the largest angle in the triangle?

 

Possible Answers:
30
108
96
60
48
Correct answer: 108
Explanation:

The measures of the three angles are x, y, and z. Because the sum of the measures of the angles in any triangle must be 180 degrees, we know that x + y + z = 180. We can use this equation, along with the other two equations given, to form this system of equations:

x + y + z = 180

y = 2z

z = 0.5x - 30

If we can solve for both y and x in terms of z, then we can substitute these values into the first equation and create an equation with only one variable.

Because we are told already that y = 2z, we alreay have the value of y in terms of z.

We must solve the equation z = 0.5x - 30 for x in terms of z.

Add thirty to both sides.

z + 30 = 0.5x

Mutliply both sides by 2

2(z + 30) = 2z + 60 = x

x = 2z + 60

Now we have the values of x and y in terms of z. Let's substitute these values for x and y into the equation x + y + z = 180.

(2z + 60) + 2z + z = 180

5z + 60 = 180

5z = 120

z = 24

Because y = 2z, we know that y = 2(24) = 48. We also determined earlier that x = 2z + 60, so x = 2(24) + 60 = 108.

Thus, the measures of the three angles of the triangle are 24, 48, and 108. The question asks for the largest of these measures, which is 108.

The answer is 108. 

Example Question #2 : Acute / Obtuse Triangles

Angles x, y, and z make up the interior angles of a scalene triangle. Angle x is three times the size of y and 1/2 the size of z. How big is angle y.

Possible Answers:

36

54

42

18

108

Correct answer:

18

Explanation:

The answer is 18

We know that the sum of all the angles is 180. Using the rest of the information given we can write the other two equations:

x + y + z = 180      

x = 3y      

2x = z

We can solve for y and z in the second and third equations and then plug into the first to solve.

x + (1/3)x + 2x = 180

3[x + (1/3)x + 2x = 180]

3x + x + 6x = 540

10x = 540

x = 54

y = 18

z = 108

Example Question #131 : Geometry

Slide2

In the picture above, \(\displaystyle \overline{AB}\) is a straight line segment. Find the value of \(\displaystyle x\).

Possible Answers:

\(\displaystyle 65\)

\(\displaystyle 70\)

\(\displaystyle 50\)

\(\displaystyle 60\)

\(\displaystyle 55\)

Correct answer:

\(\displaystyle 55\)

Explanation:

A straight line segment has 180 degrees. Therefore, the angle that is not labelled must have:

\(\displaystyle 180-110 = 70^{\circ}\)

We know that the sum of the angles in a triangle is 180 degrees. As a result, we can set up the following algebraic equation:

\(\displaystyle 70 + x + x = 180\)

Subtract 70 from both sides:

\(\displaystyle 2x = 110\)

Divide by 2:

\(\displaystyle x = 55\)

Example Question #321 : Plane Geometry

Rt_triangle_lettersIf angle \(\displaystyle a=38^\circ\) and angle \(\displaystyle c=82^\circ\), what is the value of \(\displaystyle b\)?

Possible Answers:

\(\displaystyle 60^\circ\)

\(\displaystyle 42^\circ\)

\(\displaystyle 52^\circ\)

\(\displaystyle 120^\circ\)

\(\displaystyle 60^\circ\)

Correct answer:

\(\displaystyle 60^\circ\)

Explanation:

For this problem, remember that the sum of the degrees in a triangle is \(\displaystyle 180^\circ\).

This means that \(\displaystyle a+b+c=180^\circ\).

Plug in our given values to solve:

\(\displaystyle 38^\circ+b+82^\circ=180^\circ\)

\(\displaystyle 120^\circ+b=180^\circ\)

\(\displaystyle c=60^\circ\)

Example Question #322 : Plane Geometry

In \(\displaystyle \Delta ABC\)\(\displaystyle AB = 26\)\(\displaystyle BC = 51\), and \(\displaystyle AC = 23\). To the nearest tenth, what is \(\displaystyle m \angle A\) ?

Possible Answers:

\(\displaystyle 168.5^{\circ }\)

A triangle with these sidelengths cannot exist.

\(\displaystyle 153.5^{\circ }\)

\(\displaystyle 148.5^{\circ }\)

\(\displaystyle 158.5^{\circ }\)

Correct answer:

A triangle with these sidelengths cannot exist.

Explanation:

The sum of the two smallest sides is less than the greatest side:

\(\displaystyle 26 + 23 = 49 < 51\)

By the Triangle Inequality, this triangle cannot exist.

Example Question #11 : How To Find An Angle In An Acute / Obtuse Triangle

Exterior_angle

 

If the measure of \(\displaystyle \angle A=52^{\circ}\) and the measure of \(\displaystyle \angle B= 43^{\circ}\) then what is the meausre of \(\displaystyle \angle\theta\)?

Possible Answers:

\(\displaystyle 95^{\circ}\)

Not enough information to solve

\(\displaystyle 85^{\circ}\)

\(\displaystyle 82^{\circ}\)

\(\displaystyle 98^{\circ}\)

Correct answer:

\(\displaystyle 95^{\circ}\)

Explanation:

The key to solving this problem lies in the geometric fact that a triangle possesses a total of \(\displaystyle 180^{\circ}\) between its interior angles.  Therefore, one can calculate the measure of \(\displaystyle \angle C\) and then find the measure of its supplementary angle, \(\displaystyle \angle\theta\).

\(\displaystyle 180^{\circ}=\angle A + \angle B + \angle C\)

\(\displaystyle \angle C= 180^{\circ}- 52^{\circ} - 43^{\circ}\)

\(\displaystyle \angle C= 85^{\circ}\)

\(\displaystyle \angle C\) and \(\displaystyle \angle\theta\) are supplementary, meaning they form a line with a measure of \(\displaystyle 180^{\circ}\).

\(\displaystyle \angle\theta =180^{\circ} - 85^{\circ}\)

\(\displaystyle \rightarrow 95^{\circ}\)

One could also solve this problem with the knowledge that the sum of the exterior angle of a triangle is equal to the sum of the two interior angles opposite of it.

Example Question #324 : Plane Geometry

Exterior_angle

 

 

If the measure of \(\displaystyle \angle A=56^{\circ}\) and the measure of \(\displaystyle \angle B=47^{\circ}\) then what is the meausre of \(\displaystyle \angle\theta\)?

Possible Answers:

Not enough information to solve

\(\displaystyle 103^{\circ}\)

\(\displaystyle 87^{\circ}\)

\(\displaystyle 77^{\circ}\)

\(\displaystyle 107^{\circ}\)

Correct answer:

\(\displaystyle 103^{\circ}\)

Explanation:

The key to solving this problem lies in the geometric fact that a triangle possesses a total of \(\displaystyle 180^{\circ}\) between its interior angles.  Therefore, one can calculate the measure of \(\displaystyle \angle C\) and then find the measure of its supplementary angle, \(\displaystyle \angle\theta\).

\(\displaystyle 180^{\circ}=\angle A + \angle B + \angle C\)

\(\displaystyle \angle C= 180^{\circ}- 56^{\circ} - 47^{\circ}\)

\(\displaystyle \angle C=77^{\circ}\)

\(\displaystyle \angle C\) and \(\displaystyle \angle\theta\) are supplementary, meaning they form a line with a measure of \(\displaystyle 180^{\circ}\).

\(\displaystyle \angle\theta =180^{\circ} - 77^{\circ}\)

\(\displaystyle \rightarrow 103^{\circ}\)

One could also solve this problem with the knowledge that the sum of the exterior angle of a triangle is equal to the sum of the two interior angles opposite of it.

Example Question #325 : Plane Geometry

A triangle has angles that measure \(\displaystyle 114\) and \(\displaystyle 36\) degrees. What is the measure of its third angle?

Possible Answers:

\(\displaystyle 36\) degrees

\(\displaystyle 120\) degrees

\(\displaystyle 30\) degrees

\(\displaystyle 45\) degrees

\(\displaystyle 20\) degrees

Correct answer:

\(\displaystyle 30\) degrees

Explanation:

The sum of the angles of any triangle is always \(\displaystyle 180\) degrees. Since the third angle will make up the difference between \(\displaystyle 180\) and the sum of the other two angles, add the other two angles together and subtract this sum from \(\displaystyle 180\).

Sum of the two given angles: \(\displaystyle 114 + 36 = 150\) degrees

Difference between \(\displaystyle 180\) and this sum: \(\displaystyle 180 - 150 = 30\) degrees

Example Question #2012 : Hspt Mathematics

In the triangle below, AB=BC (figure is not to scale) .  If angle A is 41°, what is the measure of angle B?

                                       A (Angle A = 41°)

                                       Act_math_108_02               

                                     B                           C

 

Possible Answers:

90

98

82

41

Correct answer:

98

Explanation:

  If angle A is 41°, then angle C must also be 41°, since AB=BC.  So, the sum of these 2 angles is:

41° + 41° = 82°

Since the sum of the angles in a triangle is 180°, you can find out the measure of the remaining angle by subtracting 82 from 180:

180° - 82° = 98°

 

 

Example Question #327 : Geometry

You are given a triangle with angles \(\displaystyle 60\) degrees and \(\displaystyle 80\) degrees. What is the measure of the third angle? 

Possible Answers:

\(\displaystyle 90\) degrees 

\(\displaystyle 70\) degrees

\(\displaystyle 80\) degrees 

\(\displaystyle 60\) degrees

\(\displaystyle 40\) degrees

Correct answer:

\(\displaystyle 40\) degrees

Explanation:

Recall that the sum of the angles of a triangle is \(\displaystyle 180\) degrees. Since we are given two angles, we can then find the third. Call our missing angle \(\displaystyle x\)

\(\displaystyle 60 + 80 + x = 180\)

We combine the like terms on the left. 

\(\displaystyle 140 + x = 180\)

Subtract \(\displaystyle 140\) from both sides.

\(\displaystyle x = 40\)

Thus, we have that our missing angle is \(\displaystyle 40\) degrees. 

 

 

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