GED Math : Angle Geometry

Study concepts, example questions & explanations for GED Math

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Example Questions

Example Question #111 : Angle Geometry

Find the measure of angle B if it is the supplement to angle A:

\displaystyle m\angle A=162^{o}

Possible Answers:

\displaystyle m\angle B=26^{o}

\displaystyle m\angle B=18^{o}

\displaystyle m\angle B=83^{o}

\displaystyle m\angle B=28^{o}

Correct answer:

\displaystyle m\angle B=18^{o}

Explanation:

If two angles are supplementary, that means the sum of their degrees of measure will add up to 180. In order to find the measure of angle B, subtract angle A from 180 like shown:

\displaystyle m\angle B=180^{o}-162^{o}=18^{o}

This gives us a final answer of 18 degrees for angle B.

Example Question #112 : Angle Geometry

Find the measure of angle B if it is the supplement to angle A:

\displaystyle m\angle A=158^{o}

Possible Answers:

\displaystyle m\angle B=24^{o}

\displaystyle m\angle B=22^{o}

\displaystyle m\angle B=26^{o}

\displaystyle m\angle B=20^{o}

Correct answer:

\displaystyle m\angle B=22^{o}

Explanation:

If two angles are supplementary, that means the sum of their degrees of measure will add up to 180. In order to find the measure of angle B, subtract angle A from 180 like shown:

\displaystyle m\angle B=180^{o}-158^{o}=22^{o}

This gives us a final answer of 22 degrees for angle B.

Example Question #1 : Opposite And Corresponding Angles

Thingy

Refer to the above diagram. 

Which of the following is a valid alternative name for \displaystyle \overrightarrow{BD} ?

Possible Answers:

\displaystyle \overrightarrow{BCD}

\displaystyle \overrightarrow{CB}

\displaystyle \overrightarrow{DB}

\displaystyle \overrightarrow{BC}

Correct answer:

\displaystyle \overrightarrow{BC}

Explanation:

The name of a ray includes two letters, so \displaystyle \overrightarrow{BCD} can be eliminated.

The first letter must be the endpoint. Since \displaystyle \overrightarrow{BD} is a name of the ray, the endpoint is \displaystyle B, and any alternative name for the ray must begin with \displaystyle B. This leaves only \displaystyle \overrightarrow{BC}.

Example Question #2 : Opposite And Corresponding Angles

 Thingy

Refer to the above diagram. 

\displaystyle \overleftrightarrow{AE} ||\overleftrightarrow{BD}\displaystyle m \angle CED = 64^{\circ }\displaystyle m \angle EFC = 107 ^{\circ }.

What is \displaystyle m \angle FCE ?

Possible Answers:

\displaystyle 64^{\circ }

\displaystyle 53^{\circ }

\displaystyle 47^{\circ }

\displaystyle 32^{\circ }

Correct answer:

\displaystyle 47^{\circ }

Explanation:

\displaystyle \angle CED and \displaystyle \angle ECD are two acute angles of a right triangle and are therefore complementary - that is, 

\displaystyle m \angle ECD + m \angle CED = 90^{\circ }

\displaystyle m \angle CED = 64^{\circ }, so

\displaystyle m \angle ECD + 64^{\circ } = 90^{\circ }

\displaystyle m \angle ECD = 26^{\circ }

\displaystyle \angle ECD and \displaystyle \angle FEC, being alternate interior angles formed by transversal \displaystyle \overrightarrow{CE} across parallel lines, are congruent, so \displaystyle m \angle FEC= 26^{\circ }.

We now look at \displaystyle \Delta FEC, whose interior angles must have degree measures totaling \displaystyle 180^{\circ }, so

\displaystyle m\angle FCE + m \angle FEC + m\angle EFC = 180^{\circ }

\displaystyle m\angle FCE + 26 ^{\circ }+107^{\circ } = 180^{\circ }

\displaystyle m\angle FCE + 133^{\circ } = 180^{\circ }

\displaystyle m\angle FCE= 47^{\circ }

Example Question #3 : Opposite And Corresponding Angles

Thingy

Refer to the above diagram.

Which of the following facts does not, by itself, prove that \displaystyle \overleftrightarrow{AE} \parallel \overleftrightarrow{BD} ?

Possible Answers:

\displaystyle \angle FED is a right angle

\displaystyle \overrightarrow{CE}  bisects \displaystyle \angle FCD

\displaystyle \angle BCE and \displaystyle \angle FEC are supplementary angles

\displaystyle \angle AFC \cong \angle DCF

Correct answer:

\displaystyle \overrightarrow{CE}  bisects \displaystyle \angle FCD

Explanation:

From the Parallel Postulate and its converse, as well as its various resulting theorems, two lines in a plane crossed by a transversal are parallel if any of the following happen:

Both lines are perpendicular to the same third line - this happens if \displaystyle \angle FED is a right angle, since, from this fact and the fact that \displaystyle \angle EDC is also right, both lines are perpendicular to \displaystyle \overline{ED}.

Same-side interior angles are supplementary - this happens if \displaystyle \angle BCE and \displaystyle \angle FEC are supplementary, since they are same-side interior angles with respect to transversal \displaystyle \overrightarrow{CE}.

Alternate interior angles are congruent - this happens if \displaystyle \angle AFC \cong \angle DCF, since they are alternate interior angles with respect to transversal \displaystyle \overleftrightarrow{FC}.

However, the fact that \displaystyle \overrightarrow{CE}  bisects \displaystyle \angle FCD has no bearing on whether \displaystyle \overleftrightarrow{AE} \parallel \overleftrightarrow{BD} is true or not, since it does not relate any two angles formed by a transversal. 

"\displaystyle \overrightarrow{CE}  bisects \displaystyle \angle FCD" is the correct choice.

Example Question #1 : Opposite And Corresponding Angles

In two intersecting lines, the opposite angles are \displaystyle (2x-7) and \displaystyle (9x-14).  What must be the value of \displaystyle x?

Possible Answers:

\displaystyle 2

\displaystyle \frac{111}{11}

\displaystyle 1

\displaystyle -3

\displaystyle \frac{201}{11}

Correct answer:

\displaystyle 1

Explanation:

In an intersecting line, vertical angles are equal to each other.

Set up an equation such that both angles are equal.

\displaystyle 2x-7 = 9x-14

Solve for \displaystyle x.  Subtract \displaystyle 2x on both sides.

\displaystyle 2x-7 -(2x)= 9x-14 -(2x)

\displaystyle -7 = 7x-14

Add 14 on both sides.

\displaystyle -7 +14= 7x-14+14

\displaystyle 7= 7x

Divide by 7 on both sides.

\displaystyle \frac{7}{7}= \frac{7x}{7}

\displaystyle x=1

The answer is:  \displaystyle 1

Example Question #4 : Opposite And Corresponding Angles

Suppose a pair of opposite angles are measured \displaystyle 2x-3 and \displaystyle 6x-8.  What must the value of \displaystyle x?

Possible Answers:

\displaystyle \frac{5}{8}

\displaystyle \frac{5}{4}

\displaystyle \frac{11}{4}

\displaystyle \frac{2}{3}

\displaystyle \frac{1}{2}

Correct answer:

\displaystyle \frac{5}{4}

Explanation:

Vertical angles are equal.

Set both angles equal and solve for x.

\displaystyle 2x-3 = 6x-8

Subtract \displaystyle 2x on both sides.

\displaystyle 2x-3 -2x= 6x-8-2x

\displaystyle -3 = 4x-8

Add 8 on both sides.

\displaystyle -3+8= 4x-8+8

\displaystyle 5=4x

Divide by 4 on both sides.

\displaystyle x=\frac{5}{4}

The answer is:  \displaystyle \frac{5}{4}

Example Question #4 : Opposite And Corresponding Angles

Suppose two vertical angles in a pair of intersecting lines.  What is the value of \displaystyle x if one angle is \displaystyle 3x-3 and the other angle is \displaystyle 33?

Possible Answers:

\displaystyle 12

\displaystyle 24

\displaystyle 50

\displaystyle 33

\displaystyle 20

Correct answer:

\displaystyle 12

Explanation:

Vertical angles of intersecting lines must equal to each other.

Set up an equation such that both angle measures are equal.

\displaystyle 3x-3 = 33

Add three on both sides.

\displaystyle 3x-3 +3= 33+3

\displaystyle 3x =36

Divide by three on both sides.

\displaystyle \frac{3x }{3}=\frac{36}{3}

The answer is:  \displaystyle 12

Example Question #544 : 2 Dimensional Geometry

Suppose two opposite angles are measured \displaystyle 5x-5 and \displaystyle 75. What is the value of \displaystyle 2x?

Possible Answers:

\displaystyle 28

\displaystyle 16

\displaystyle 32

\displaystyle \textup{The answer is not given.}

\displaystyle 14

Correct answer:

\displaystyle 32

Explanation:

Opposite angles equal.  Set up an equation such that both angle values are equal.

\displaystyle 5x-5 =75

Add 5 on both sides.

\displaystyle 5x-5 +5=75 +5

\displaystyle 5x = 80

Divide by 5 on both sides.

\displaystyle \frac{5x}{5} = \frac{80}{5}

\displaystyle x=16

\displaystyle 2x =32

The answer is:  \displaystyle 32

Example Question #4 : Opposite And Corresponding Angles

With a pair of intersecting lines, a set of opposite angles are measured \displaystyle 5x+1 and \displaystyle 10x-9.  What must the value of \displaystyle 7x be?

Possible Answers:

\displaystyle 9

\displaystyle 14

\displaystyle 2

\displaystyle 21

\displaystyle \frac{56}{5}

Correct answer:

\displaystyle 14

Explanation:

Opposite angles of two intersecting lines must equal to each other. Set up an equation such that both angle are equal.

\displaystyle 5x+1= 10x-9

Add 9 on both sides.

\displaystyle 5x+1+9= 10x-9+9

\displaystyle 5x+10= 10x

Subtract \displaystyle 5x on both sides.

\displaystyle 5x+10-5x= 10x-5x

\displaystyle 10 = 5x

\displaystyle x=2

This means that \displaystyle 7x equals \displaystyle 14.

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