Find 4th Angle of Quadrilateral

Find Unknown Angles: Learn

A quadrilateral is any four-sided shape. These shapes also have exactly 4 interior angles. The sum of the interior angles of a quadrilateral are equal to 3600°. That is, all 4 of the angles in a quadrilateral should add up to 3600°.

When three angles are known but the fourth is unknown, we can calculate the unknown angle. To find the fourth unknown angle of a quadrilateral, subtract the number of degrees in the other three angles from 360°.

Example: How many degrees are in the fourth angle of a quadrilateral whose other angles are 80°, 90°, and 65°?

Answer: 360° - 40° - 90° - 65° = 125°

Find Unknown Angles: Practice


What is the unknown angle of a quadrilateral whose known angles are
°, °, and °?


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