Question

a side of the triangle below has been extended to form an exterior angle of 149°. find the value of x.

Explanation:

Step1: Find adjacent interior angle

The exterior angle and its adjacent interior angle are supplementary, so subtract the exterior angle from 180°.
$180^\circ - 149^\circ = 31^\circ$

Step2: Calculate $x$ using triangle angles

The triangle is right-angled, so the sum of the two non-right angles is 90°. Subtract the angle from Step1 from 90°.
$x = 90^\circ - 31^\circ$

Answer:

$59^\circ$