# How to Prove an Angle is at 90 Degrees?

In mathematics, an angle is defined as two rays that share the same endpoint. The point where the rays meet, or intersect, is called the vertex. The two rays, or line segments, are considered the s... Read More »
http://www.ehow.com/how_8310334_prove-angle-90-degrees.html

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## How to Prove Angle-Angle Similarity?

A proof for an angle-angle similarity requires three steps to show that two different angles on two triangles are congruent. Because the triangles have two congruent angles, the triangles are simil... Read More »
http://www.ehow.com/how_8438932_prove-angleangle-similarity.html

## How to Prove a Right Angle in Math?

A right angle is a 90 degree angle that forms where perpendicular 180 degree lines meet or cross. Proving that a polygon such as a square, rectangle or triangle has a right angle requires knowledge... Read More »
http://www.ehow.com/how_8151138_prove-right-angle-math.html

## How to Prove the Angle Sum Property of a Triangle?

To prove that the sum of all angles of a triangle is 180 degrees, follow these steps. Let's take a triangle ABC .
http://www.wikihow.com/Prove-the-Angle-Sum-Property-of-a-Triangle

## How does height affect angle ie a 90 degree roof angle at a 20 degree pitch with a building That projects 10 degrees what angle does the building meet the roof?

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