Question

In a right triangle that has one acute angle of 18 degrees, cos 18 degrees is congruent to ?

Answer 1

cos(18°)=sin(72°)

Explanation:

we know that

In a right triangle

cos(A)=sin(B)

If A and B are complementary angles

so

A+B=90°

In this problem

A=18°

B=90-18=72°

therefore

cos(18°)=sin(72°)