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If sin x = 1213 and sin y = \(\frac{4}{5}\...

If sin x = 1213 and sin y = 45, where x and y are acute angles, find  cos (x + y)

A.

4865

B.

1315

C.

3365

D.

4865

Correct answer is C

From Pythagoras' theorem

when sin x = 1213, cos x = 513

Using cos (x + y) = cosx cosy - sinxsiny

51335121345

3365