GED Math : 2-Dimensional Geometry

Study concepts, example questions & explanations for GED Math

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Example Questions

Example Question #541 : 2 Dimensional Geometry

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

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

Possible Answers:

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

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

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

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

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 #542 : 2 Dimensional Geometry

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

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

Possible Answers:

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

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

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

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

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 #543 : 2 Dimensional Geometry

Thingy

Refer to the above diagram. 

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

Possible Answers:

\(\displaystyle \overrightarrow{DB}\)

\(\displaystyle \overrightarrow{CB}\)

\(\displaystyle \overrightarrow{BCD}\)

\(\displaystyle \overrightarrow{BC}\)

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:

\(\displaystyle 53^{\circ }\)

\(\displaystyle 64^{\circ }\)

\(\displaystyle 32^{\circ }\)

\(\displaystyle 47^{\circ }\)

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 #544 : 2 Dimensional Geometry

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

\(\displaystyle \angle AFC \cong \angle DCF\)

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

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

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 #4 : 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:

\(\displaystyle 2\)

\(\displaystyle 1\)

\(\displaystyle -3\)

\(\displaystyle \frac{201}{11}\)

\(\displaystyle \frac{111}{11}\)

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 #5 : 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:

\(\displaystyle \frac{11}{4}\)

\(\displaystyle \frac{1}{2}\)

\(\displaystyle \frac{5}{8}\)

\(\displaystyle \frac{5}{4}\)

\(\displaystyle \frac{2}{3}\)

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 #6 : 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:

\(\displaystyle 12\)

\(\displaystyle 20\)

\(\displaystyle 24\)

\(\displaystyle 33\)

\(\displaystyle 50\)

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 #545 : 2 Dimensional Geometry

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

Possible Answers:

\(\displaystyle 28\)

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

\(\displaystyle 32\)

\(\displaystyle 14\)

\(\displaystyle 16\)

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 #546 : 2 Dimensional Geometry

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:

\(\displaystyle 21\)

\(\displaystyle 9\)

\(\displaystyle \frac{56}{5}\)

\(\displaystyle 14\)

\(\displaystyle 2\)

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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