Question

How are the sin 20° and the cos 70° related?

Answer 1

sin 20=cos(90-20)=cos 70

Answer 2

they are equal to each other

Answer 3

You can see that when they add upto 90 they mean equal values.
20+70=90

Answer 4

sin and cos are cofunctions, so the sin of one acute angle of a right triangle equals the cos of the other acute angle of a right triangle.