High School Math : Geometry

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #1 : How To Find An Angle In An Acute / Obtuse Triangle

In a given triangle, the angles are in a ratio of 1:3:5.  What size is the middle angle?

Possible Answers:

45^{\circ}

60^{\circ}

20^{\circ}

75^{\circ}

90^{\circ}

Correct answer:

60^{\circ}

Explanation:

Since the sum of the angles of a triangle is 180^{\circ}, and given that the angles are in a ratio of 1:3:5, let the measure of the smallest angle be , then the following expression could be written:

x+3x+5x=180

9x=180

x=20

 

If the smallest angle is 20 degrees, then given that the middle angle is in ratio of 1:3, the middle angle would be 3 times as large, or 60 degrees.

Example Question #431 : Psat Mathematics

Triangle ABC has angle measures as follows:

\dpi{100} \small m\angle ABC=4x+3 

\dpi{100} \small m\angle ACB=2x+6

\dpi{100} \small m\angle BAC=3x

What is \dpi{100} \small m\angle BAC?

Possible Answers:

79

19

44

57

90

Correct answer:

57

Explanation:

The sum of the measures of the angles of a triangle is 180.

Thus we set up the equation \dpi{100} \small 4x+3+2x+6+3x=180

After combining like terms and cancelling, we have \dpi{100} \small 9x=171\rightarrow x=19

Thus \dpi{100} \small m\angle BAC=3x=57

Example Question #431 : Psat Mathematics

The base angle of an isosceles triangle is five more than twice the vertex angle.  What is the base angle?

Possible Answers:

55

47

62

73

34

Correct answer:

73

Explanation:

Every triangle has 180 degrees.  An isosceles triangle has one vertex angle and two congruent base angles.

Let x = the vertex angle and 2x+5 = the base angle

So the equation to solve becomes  x+(2x+5)+(2x+5)=180

Thus the vertex angle is 34 and the base angles are 73.

Example Question #1 : How To Find An Angle In An Acute / Obtuse Triangle

The base angle of an isosceles triangle is 15 less than three times the vertex angle.  What is the vertex angle?

Possible Answers:

Correct answer:

Explanation:

Every triangle contains 180 degrees.  An isosceles triangle has one vertex angle and two congruent base angles.

Let  = vertex angle and  = base angle

So the equation to solve becomes .

Example Question #1 : How To Find An Angle In An Acute / Obtuse Triangle

The base angle of an isosceles triangle is ten less than twice the vertex angle.  What is the vertex angle?

Possible Answers:

Correct answer:

Explanation:

Every triangle has 180 degrees.  An isosceles triangle has one vertex angle and two congruent base angles.

Let  = vertex angle and  = base angle

So the equation to solve becomes 

So the vertex angle is 40 and the base angles is 70

Example Question #141 : Triangles

The base angle of an isosceles triangle is 10 more than twice the vertex angle.  What is the vertex angle?

Possible Answers:

Correct answer:

Explanation:

Every triangle has 180 degrees.  An isosceles triangle has one vertex angle and two congruent base angles.

Let = the vertex angle and  = the base angle

So the equation to solve becomes

The vertex angle is 32 degrees and the base angle is 74 degrees

Example Question #432 : Geometry

In an isosceles triangle, the vertex angle is 15 less than the base angle.  What is the base angle?

Possible Answers:

Correct answer:

Explanation:

Every triangle has 180 degrees.  An isosceles triangle has one vertex angle and two congruent base angles.

Let  = base angle and  = vertex angle

So the equation to solve becomes

Thus, 65 is the base angle and 50 is the vertex angle.

Example Question #11 : Isosceles Triangles

In an isosceles triangle the vertex angle is half the base angle.  What is the vertex angle?

Possible Answers:

108

54

45

36

72

Correct answer:

36

Explanation:

Every triangle has 180 degrees.  An isosceles triangle has one vertex angle and two congruent base angles.

Let x = base angle and 0.5x = vertex angle

So the equation to solve becomes x+x+0.5x=180, thus x=72 is the base angle and 0.5x=36 is the vertex angle.

Example Question #1 : How To Find An Angle In An Acute / Obtuse Triangle

If the average of the measures of two angles in a triangle is 75o, what is the measure of the third angle in this triangle?

Possible Answers:

75°

40°

30°

65°

50°

Correct answer:

30°

Explanation:

The sum of the angles in a triangle is 180o:  a + b + c = 180

In this case, the average of a and b is 75:

(a + b)/2 = 75, then multiply both sides by 2

(a + b) = 150, then substitute into first equation

150 + c = 180

c = 30

Example Question #231 : Plane Geometry

Which of the following can NOT be the angles of a triangle?

Possible Answers:

45, 90, 100

30, 60, 90

1, 2, 177

30.5, 40.1, 109.4

45, 45, 90

Correct answer:

45, 90, 100

Explanation:

In a triangle, there can only be one obtuse angle. Additionally, all the angle measures must add up to 180.

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