Question

which angle is complementary to ∠1?

Explanation:

Step1: Recall complementary angles definition

Two angles are complementary if their sum is 90 degrees.

Step2: Observe the figure

We see that $\angle1+\angle2 = 90^{\circ}$ (since $\angle3$ is a right - angle and the angles around the intersection are related such that the non - overlapping angles $\angle1$ and $\angle2$ make up a right - angle).

Answer:

$\angle2$