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Question-74446




Question Number 74446 by rajesh4661kumar@gmail.com last updated on 24/Nov/19
Answered by Kunal12588 last updated on 24/Nov/19
I=∫e^(tan^(−1) x) (((1+x+x^2 )/(1+x^2 )))dx  let t=tan^(−1) x  ⇒dt=(dx/(1+x^2 ))  I=∫e^t (1+tan t + tan^2  t)dt  ⇒I=∫e^t (tan t + sec^2  t)dt  ⊛  ⇒I=e^t tan t +C  ⇒I=xe^(tan^(−1) x)  +C  ⊛ ∫e^x [f(x)+f ′(x)]dx=e^x f(x)+C
$${I}=\int{e}^{{tan}^{−\mathrm{1}} {x}} \left(\frac{\mathrm{1}+{x}+{x}^{\mathrm{2}} }{\mathrm{1}+{x}^{\mathrm{2}} }\right){dx} \\ $$$${let}\:{t}={tan}^{−\mathrm{1}} {x} \\ $$$$\Rightarrow{dt}=\frac{{dx}}{\mathrm{1}+{x}^{\mathrm{2}} } \\ $$$${I}=\int{e}^{{t}} \left(\mathrm{1}+{tan}\:{t}\:+\:{tan}^{\mathrm{2}} \:{t}\right){dt} \\ $$$$\Rightarrow{I}=\int{e}^{{t}} \left({tan}\:{t}\:+\:{sec}^{\mathrm{2}} \:{t}\right){dt}\:\:\circledast \\ $$$$\Rightarrow{I}={e}^{{t}} {tan}\:{t}\:+{C} \\ $$$$\Rightarrow{I}={xe}^{{tan}^{−\mathrm{1}} {x}} \:+{C} \\ $$$$\circledast\:\int{e}^{{x}} \left[{f}\left({x}\right)+{f}\:'\left({x}\right)\right]{dx}={e}^{{x}} {f}\left({x}\right)+{C} \\ $$
Commented by Kunal12588 last updated on 24/Nov/19
∫e^x [f(x)+f ′(x)]dx  =∫e^x f(x)dx+∫e^x f ′(x) dx  =e^x f(x)−∫e^x f ′(x)dx+∫e^x f ′(x)dx  =e^x f(x)+C
$$\int{e}^{{x}} \left[{f}\left({x}\right)+{f}\:'\left({x}\right)\right]{dx} \\ $$$$=\int{e}^{{x}} {f}\left({x}\right){dx}+\int{e}^{{x}} {f}\:'\left({x}\right)\:{dx} \\ $$$$={e}^{{x}} {f}\left({x}\right)−\int{e}^{{x}} {f}\:'\left({x}\right){dx}+\int{e}^{{x}} {f}\:'\left({x}\right){dx} \\ $$$$={e}^{{x}} {f}\left({x}\right)+{C} \\ $$

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