Question

In the figure, ABCD is a cyclic quadrilateral, Find the value of x.

Answer 1

$\angle CDE+\angle CDA={180}^o$ (Linear pair)

$\Rightarrow {80}^o+\angle CDA={180}^o$

$\Rightarrow \angle CDA={180}^o-{80}^o={100}^o$

In cyclic quadrilateral ABCD,

Ext. $\angle ABF=$ Its interior opposite angle $\angle CDA={100}^o$

$\therefore x={100}^o$