Question

In the triangle ABC, B is the right angle. If sin A = 8/17, what is cos C?

Answer 1

Answer:  8/17

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Explanation:

The rule is

If A+C = 90, then sin(A) = cos(C). We could also say cos(A) = sin(C).

I recommend drawing out the picture of what's going on. See below.

sin(A) = 8/17 has the opposite side 8 over hypotenuse 17.

cos(C) = 8/17 has 8 as the adjacent side now. The hypotenuse stays the same.

So that's why sin(A) = cos(C).