If `y=e^-x cos x`, show that `(d^2y)/(dx^2)= 2e^-1 sin x`

1.	If `y=e^-x cos x`, show that `(d^2y)/(dx^2)= 2e^-1 sin x`
Answer» `y=e^(-x)cosx` diff. with respect to x `dy/dx=-e^(-x)cosx-e^x sinx` diff. with respect to x `(d^2y)/(dx^2)=-[-e^(-x)cosx+e^(-x)(-sinx)]-[-e^(-x)sinx+e^(-x)cosx]` `=e^(-x)cosxx+e^(-x)sinx+e^(-x)sinxx-e^(-x)cosx` `=2e^(-x)sinx`.

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