Question

Find the value of the unknown exterior angle $x$ in the following diagrams.

Answer 1

Sum of all angles of a $\Delta ={180}^o$

${30}^o+{60}^o+\angle ACB={180}^o$

$\therefore \angle ACB={90}^o$

Now, $x+\angle ACB={90}^o$

$\therefore x={90}^o$

OR

Since, Exterior angle $=$ Sum of interior opposite angles, therefore $x={60}^o+{30}^o={90}^o$.