Question

Question 170
Three angles of a quadrilateral are equal. The fourth angle is ${120}^{\circ }$. What is the measure of equal angles?

Answer 1

Let the measure of equal angles be $x^{\circ }$ each.
Then, by the angle sum property of a quadrilateral, we have
$x^{\circ }+x^{\circ }+x^{\circ }+{120}^{\circ }={360}^{\circ }\Rightarrow 3x^{\circ }+{120}^{\circ }={360}^{\circ }\Rightarrow 3x^{\circ }={240}^{\circ }\Rightarrow x^{\circ }={80}^{\circ }$