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## Homework Statement

For each n, let y^(n) denote the nth derivative of the function y = e^(x) cosx.

Can you suggest a general formula for y^(k), where k is an interger > 0? What is y^(2010)?

## Homework Equations

None

## The Attempt at a Solution

I got e^(x) (cosx - sinx) for y'

-2e^(x) sinx for y''

-2e^(x) (cosx + sinx) for y''' and

-4e^(x) cosx for y''''

which are right, but I dont see a pattern for the nth derivative, which could help me answer the question.