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Find the exact value of: cos315.

I have to use the sum angle formula
cos(270+45)
cos270 cos45 - sin270 sin45
thats all I have. Is the answer at least sqrt 2/2?

1 answer

Use the facts that
cos 270 = 0
sin 270 = -1, and
and sin 45 = cos 45 = (sqrt2)/2 to complete the problem

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