Math CentralQuandaries & Queries


Question from Kristine, a student:

Find measure of unknown side

Hi Kristine,

Suppose you have a right triangle. The side opposite the right angle is called the hypotenuse. Let A is one of the angles, not the right angle. The other two sides are given names relative to A. The side close to A is called the adjacent side and the third side is called the side opposite to A.


The cosine of the angle A is defined to be the length of the adjacent side divided by the length of the hypotenuse, so

cos A = adjacent/hypotenuse.

Since you know that cos A = 0.5 if you know either the length of the adjacent side or the length of the hypotenuse you can find the other.

I hope this helps,

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