\[\frac{d}{dx} x{e}^{x}\cos{x}\]

1
Use Product Rule to find the derivative of xexcosxx{e}^{x}\cos{x}. The product rule states that (fg)=fg+fg(fg)'=f'g+fg'.
(ddxx)excosx+x(ddxex)cosx+xex(ddxcosx)(\frac{d}{dx} x){e}^{x}\cos{x}+x(\frac{d}{dx} {e}^{x})\cos{x}+x{e}^{x}(\frac{d}{dx} \cos{x})

2
Use Power Rule: ddxxn=nxn1\frac{d}{dx} {x}^{n}=n{x}^{n-1}.
excosx+x(ddxex)cosx+xex(ddxcosx){e}^{x}\cos{x}+x(\frac{d}{dx} {e}^{x})\cos{x}+x{e}^{x}(\frac{d}{dx} \cos{x})

3
The derivative of ex{e}^{x} is ex{e}^{x}.
excosx+xexcosx+xex(ddxcosx){e}^{x}\cos{x}+x{e}^{x}\cos{x}+x{e}^{x}(\frac{d}{dx} \cos{x})

4
Use Trigonometric Differentiation: the derivative of cosx\cos{x} is sinx-\sin{x}.
excosx+xexcosxxexsinx{e}^{x}\cos{x}+x{e}^{x}\cos{x}-x{e}^{x}\sin{x}

Done

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