Q67 of 354 Page 11

If y = ex cos x, prove that .

Given y = excos(x)


On differentiating y with respect to x, we get




Recall that (uv)’ = vu’ + uv’ (product rule)



We know and


[chain rule]







We know



However, cos(A)cos(B) – sin(A)sin(B) = cos(A + B)



Thus,


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