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The Complete Idiot's Guide to Trigonometry by Izolda Fotiyeva, Dmitriy Fotiyev

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Right Triangles

Let’s start our study of triangles with discussing the three main types of angles. These types are acute angles, right angles, and obtuse angles.

img DEFINITION

An acute angle is an angle with a measure less than 90º.

A right angle is an angle with a measure of 90º.

An obtuse angle is an angle with a measure greater than 90º.

Recall from geometry that you need three known measures to describe a triangle—the lengths of two sides and the measure of an angle, the lengths of three sides, or three other measures. For a right triangle, you need only two additional measures, because you already know that one of the angles’ measures is ...

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