GED Math : Angles and Triangles

Study concepts, example questions & explanations for GED Math

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Example Questions

Example Question #1 : Angles And Triangles

Which of the following can be the measures of the three angles of an acute isosceles triangle?

Possible Answers:

\displaystyle 80 ^{\circ }, 80 ^{\circ }, 40 ^{\circ }

\displaystyle 36^{\circ }, 72 ^{\circ }, 72 ^{\circ }

\displaystyle 32 ^{\circ }, 32 ^{\circ }, 116^{\circ }

\displaystyle 45 ^{\circ }, 45 ^{\circ }, 90^{\circ }

\displaystyle 50 ^{\circ }, 60 ^{\circ }, 70 ^{\circ }

Correct answer:

\displaystyle 36^{\circ }, 72 ^{\circ }, 72 ^{\circ }

Explanation:

For the triangle to be acute, all three angles must measure less than \displaystyle 90 ^{\circ }. We can eliminate \displaystyle 32 ^{\circ }, 32 ^{\circ }, 116^{\circ } and \displaystyle 45 ^{\circ }, 45 ^{\circ }, 90^{\circ } for this reason. 

In an isosceles triangle, at least two angles are congruent, so we can eliminate \displaystyle 50 ^{\circ }, 60 ^{\circ }, 70 ^{\circ }.

The degree measures of the three angles of a triangle must total 180, so, since \displaystyle 80 ^{\circ }+ 80 ^{\circ }+ 40 ^{\circ } = 200^{\circ }, we can eliminate \displaystyle 80 ^{\circ }, 80 ^{\circ }, 40 ^{\circ }.

\displaystyle 36^{\circ }, 72 ^{\circ }, 72 ^{\circ } is correct.

Example Question #1 : Angles And Triangles

Triangle

Note: Figure NOT drawn to scale.

Refer to the above triangle. Evaluate \displaystyle x.

Possible Answers:

\displaystyle x = 31

\displaystyle x = 39

\displaystyle x = 63

\displaystyle x = 51

Correct answer:

\displaystyle x = 39

Explanation:

The degree measures of a triangle total \displaystyle 180^{\circ }, so

\displaystyle x + (x+24) + 2x = 180

\displaystyle 4x+24 = 180

\displaystyle 4x+24 -24 = 180 -24

\displaystyle 4x = 156

\displaystyle 4x \div 4 = 156 \div 4

\displaystyle x = 39

Example Question #52 : Triangles

Triangle

Note: Figure NOT drawn to scale.

Refer to the above figure. Evaluate \displaystyle y.

Possible Answers:

\displaystyle y = 41

\displaystyle y = 56 \frac{1}{2}

\displaystyle y = 20 \frac{1}{2}

\displaystyle y = 31

Correct answer:

\displaystyle y = 56 \frac{1}{2}

Explanation:

The degree measures of the interior angles of a triangle total \displaystyle 180 ^{\circ }, so, if we let \displaystyle x^{\circ } be the measure of the unmarked angle, then

\displaystyle x + 41 + 72 = 180

\displaystyle x + 113 = 180

\displaystyle x = 67

Three angles with measures \displaystyle 67^{\circ}, y^{\circ}, y^{\circ} together form a straight angle, so

\displaystyle y+ y + 67= 180

\displaystyle 2y+ 67= 180

\displaystyle 2y+ 67- 67 = 180 - 67

\displaystyle 2y = 113

\displaystyle 2y \div 2 = 113 \div 2

\displaystyle y = 56 \frac{1}{2}

Example Question #232 : 2 Dimensional Geometry

Thingy

Figure drawn to scale.

Refer to the above diagram. 

Which of the following is a valid description of \displaystyle \Delta EFC ?

Possible Answers:

Right

Acute

Equiangular

Obtuse

Correct answer:

Obtuse

Explanation:

One of the angles of \displaystyle \Delta EFC - namely, \displaystyle \angle EFC - can be seen to be an obtuse angle, as it is wider than a right angle. This makes \displaystyle \Delta EFC, by definition, an obtuse triangle.

Example Question #1 : Angles And Triangles

Thingy

Refer to the above diagram. 

Which of the following is a valid description of \displaystyle \Delta CED ?

Possible Answers:

Obtuse

Equiangular

Right

Acute

Correct answer:

Right

Explanation:

One of the angles of \displaystyle \Delta CED - namely, \displaystyle \angle CDE - is marked as a right angle. This makes \displaystyle \Delta CED, by definition, a right triangle.

Example Question #1202 : Ged Math

Which of the following follows from the fact that \displaystyle \Delta MNO \cong \Delta PQR?

Possible Answers:

\displaystyle \angle O \cong \angle Q

\displaystyle \angle N \cong \angle R

\displaystyle \angle M \cong \angle P

\displaystyle \angle M \cong \angle N

Correct answer:

\displaystyle \angle M \cong \angle P

Explanation:

A congruency statement about two triangles implies nothing about the relationship between two angles of one of the triangles, so \displaystyle \angle M \cong \angle N is not correct.

Also, letters in the same position between the two triangles refer to corresponding - and subsequently, congruent - angles. Therefore, \displaystyle \Delta MNO \cong \Delta PQR implies that:

\displaystyle \angle M \cong \angle P

\displaystyle \angle N \cong \angle Q

\displaystyle \angle O \cong \angle R

Of the given choices, only \displaystyle \angle M \cong \angle P is a consequence. It is the correct response.

Example Question #1 : Angles And Triangles

An exterior angle of an isosceles triangle measures \displaystyle 130 ^{\circ }. What is the greatest measure of any of the three angles of the triangle?

Possible Answers:

\displaystyle 50^{\circ }

Insufficient information is given to answer this question.

\displaystyle 80 ^{\circ }

\displaystyle 65 ^{\circ }

Correct answer:

Insufficient information is given to answer this question.

Explanation:

The triangle has an exterior angle of \displaystyle 130 ^{\circ }, so it has an interior angle of \displaystyle (180-130)^{\circ } = 50^{\circ }. By the Isosceles Triangle Theorem, an isosceles triangle must have two congruent angles; there are two possible scenarios that fit this criterion:

Case 1: Two angles have measure \displaystyle 50^{\circ }. The third angle will have measure

\displaystyle \left [180 - (50 + 50 ) \right ] ^{\circ } = 80 ^{\circ }.

\displaystyle 80 ^{\circ } will be the greatest of the angle measures.

Case 2: One angle has measure \displaystyle 50^{\circ } and the others are congruent. Their common measure will be

\displaystyle \frac{1}{2} (180^{\circ }- 50^{\circ } ) = 65 ^{\circ }.

\displaystyle 65 ^{\circ } will be the greatest of the angle measures.

The given information is therefore inconclusive.

Example Question #64 : Triangles

An exterior angle of an isosceles triangle measures \displaystyle 130 ^{\circ }. What is the least measure of any of the three angles of the triangle?

Possible Answers:

\displaystyle 80 ^{\circ }

Insufficient information is given to answer this question

\displaystyle 65 ^{\circ }

\displaystyle 50^{\circ }

Correct answer:

\displaystyle 50^{\circ }

Explanation:

The triangle has an exterior angle of \displaystyle 130 ^{\circ }, so it has an interior angle of \displaystyle (180-130)^{\circ } = 50^{\circ }. By the Isosceles Triangle Theorem, an isosceles triangle must have two congruent angles; there are two possible scenarios that fit this criterion:

Case 1: Two angles have measure \displaystyle 50^{\circ }. The third angle will have measure

\displaystyle \left [180 - (50 + 50 ) \right ] ^{\circ } = 80 ^{\circ }.

\displaystyle 50^{\circ } will be the least of the angle measures.

Case 2: One angle has measure \displaystyle 50^{\circ } and the others are congruent. Their common measure will be

\displaystyle \frac{1}{2} (180^{\circ }- 50^{\circ } ) = 65 ^{\circ }.

\displaystyle 50^{\circ } will be the least of the angle measures.

In both cases, the least of the degree measures of the angles will be \displaystyle 50^{\circ }.

Example Question #2 : Angles And Triangles

An exterior angle of an isosceles triangle measures \displaystyle 70 ^{\circ }. What is the least measure of any of the three angles of the triangle?

Possible Answers:

Insufficient information is given to answer this question.

\displaystyle 70^{\circ }

\displaystyle 35 ^{\circ }

\displaystyle 40^{\circ }

Correct answer:

\displaystyle 35 ^{\circ }

Explanation:

The triangle has an exterior angle of \displaystyle 70 ^{\circ }, so it has an interior angle of \displaystyle (180-70)^{\circ } = 110 ^{\circ }.

Since this is an obtuse angle, its other two angles must be acute. By the Isosceles Triangle Theorem, an isosceles triangle must have two congruent angles - the acute angles are those. Since the sum of their measures is the same as their remote exterior angle - \displaystyle 70 ^{\circ } - each has measure \displaystyle 35 ^{\circ }.This is the correct response.

Example Question #5 : Angles And Triangles

An exterior angle of an isosceles triangle measures \displaystyle 80 ^{\circ }. What is the greatest measure of any of the three angles of the triangle?

Possible Answers:

Insufficient information is given to answer this question.

\displaystyle 100 ^{\circ }

\displaystyle 40^{\circ }

\displaystyle 80^{\circ }

Correct answer:

\displaystyle 100 ^{\circ }

Explanation:

The triangle has an exterior angle of \displaystyle 80 ^{\circ }, so it has an interior angle of \displaystyle (180-80)^{\circ } = 100 ^{\circ }.

Since this is an obtuse angle, its other two angles must be acute. Therefore, this angle is the one of greatest measure.

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