How to Find Missing Angels in Quadrilateral Shapes? (+FREE Worksheet!)

The parallelogram is a simple quadrilateral with two pairs of parallel sides. The size of the opposite sides and the opposite angles in the parallelogram are equal. \({\angle}A+{\angle}B+{\angle}C+{\angle}D=360^{\circ}\).

Find the missing angle in the quadrilateral.

Solution: We have been given three angles and need to determine the measure of the fourth. Add together the measures of the known angles.

\(125^{\circ}+90^{\circ}+105^{\circ}=320^{\circ}\)

Subtract the sum from \(360^{\circ}\) to determine what remains for the fourth angle. \(360^{\circ}-320^{\circ}=40^{\circ}\)

The measure of the unknown angle is \(40^{\circ}\)

Find the missing angle in the quadrilateral.

Solution: We have been given three angles and need to determine the measure of the fourth. Add together the measures of the known angles.

\(78^{\circ}+85^{\circ}+57^{\circ}=220^{\circ}\)

Subtract the sum from \(360^{\circ}\) to determine what remains for the fourth angle. \(360^{\circ}-220^{\circ}=140^{\circ}\)

The measure of the unknown angle is \(140^{\circ}\)