Question

if 1/5 of a 90 - degree angle
1
72° 57°
3
2 4
9
45
90
18

Explanation:

Step1: Find angle 1

The large triangle is a right - triangle. One non - right angle is 72°. So, angle 1 = 90° - 72° = 18°.

Step2: Find angle 2

In the small triangle, one angle is 57° and another (the one adjacent to the 72° angle in the large triangle) is 18°. Using the angle - sum property of a triangle (sum of angles in a triangle is 180°), angle 2=180°-(57° + 18°)=105°. But this is not relevant to the final answer.

Step3: Find the required angle

We want 1/5 of a 90 - degree angle. $\frac{1}{5}\times90° = 18°$.

Answer:

18