# Trig

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given that sinx=3/4 and cosy=-5/13 and both x and y are in quadrant II, find the exact value of cos(x-y)

• Trig -

cos (x-y) = cos x cos y = sin x sin y
cos x = -sqrt7 /4
cos y = -5/13
sin x = 3/4
sin y = 12/13
so

cos(x-y)=5sqrt7/52 - 9/13

• Trig -

sorry typo
cos x cos y + sin x sin y
5 sqrt 7/52 + 9/13
= .9467

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