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## Homework Statement

It bascially says when the sum of two angles are 90 deg they are complimentary....

Then it goes on saying

sin(90-theta) = cos theta

and so on.....

I understand the concept such as if sin(30) = cos(60)

But the book doesnt explain why it works.. it just says if two compl angles are 90 deg then sin(90-theta) = cos theta, which is not an explanation at all...

can some one help me understand why this is?

Thank you.