SAT Math : How to find the length of the side of an acute / obtuse triangle

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #21 : Acute / Obtuse Triangles

Given  with  and .

Which of the following could be the correct ordering of the lengths of the sides of the triangle?

I) 

II) 

III) 

Possible Answers:

II only

II or III only

I only

I or II only

III only

Correct answer:

II or III only

Explanation:

Given two angles of unequal measure in a triangle, the side opposite the greater angle is longer than the side opposite the other angle.

If  were the angle of greatest measure, then , and

.

Since the measures of the angles must total  cannot have the greatest measure.

, so we can explore two other possibilities:

, which here is possible if, for example, 

 and  - since ; and,

, which here is possible if, for example, 

 and  - since .

If , then ; if , then .

This makes the correct response II or III only.

Example Question #152 : Geometry

Which of the given answers choices could NOT represent the sides of a triangle?

Possible Answers:

All of the given answers could represent the sides of a triangle. 

Correct answer:

Explanation:

In order for three lengths to represent the sides of a triangle, they must pass the Triangle Inequality. 

This means that the sum of any two sides of the triangle must exceed the length of the third side. 

With the given answers, the one set of lengths that fail this test is 

Therefore, the lengths  could not represent the sides of a triangle. 

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