Q1 of 109 Page 287

Three angles of a quadrilateral measure 56°, 115° and 84°. Find the measure of the fourth angle.

Let the measure of the fourth angle be xo.
Since the sum of the angles of a quadrilateral is 360°, we have:
∴ 56° + 115° + 84° + x° = 360°
 ∴ 255° + x° = 360° ​
∴ x° = 105°
Hence, the measure of the fourth angle is 105°.


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