Question

a side of the triangle below has been extended to form an exterior angle of 72°. find the value of x.

Explanation:

Step1: Recall exterior - angle property

The exterior angle of a triangle is equal to the sum of the two non - adjacent interior angles.
Let the non - adjacent interior angles be $x$ and $55^{\circ}$, and the exterior angle be $72^{\circ}$. So, $x + 55^{\circ}=72^{\circ}$.

Step2: Solve for $x$

Subtract $55^{\circ}$ from both sides of the equation: $x=72^{\circ}- 55^{\circ}$.

Answer:

$17^{\circ}$