Evaluate: `inte^(x)cosx\ dx`

Explanation

Let `I =int e^{x} cos x d x`
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I=cos x cdot int e^{x} d x-int[(cos x)^{prime} cdot int e^{x} d x] `
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I=cos x . e^{x}+int sin x cdot e^{x} d x`
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I=cos x . e^{x}+sin x . int e^{x} d x-int(sin x)^{prime} int e^{x} d x`
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I=cos x cdot e^{x}+sin x cdot e^{x}-int cos x cdot e^{x} d x`
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I=e^{x}(cos x+sin x)-I`
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