Question

Three angles of a quadrilateral are equal to ${100}^{\circ },{60}^{\circ }$ and ${80}^{\circ }$, respectively. Find its fourth angle.

Answer 1

The given three angles of the quadrilateral are ${100}^o,{60}^o$ and ${80}^o$.

Let the fourth angle be $x$,

We know that, the sum of all interior angles of a quadrilateral is ${360}^o$

Hence, $x+{100}^o+{60}^o+{80}^o={360}^o$

$x+{240}^o={360}^o$

$x={360}^o-{240}^o$

$x={120}^o$

Hence, the fourth angle of quadrilateral is ${120}^o$.