$f(x)=e^x \sin x$, then $f^{(6)}(x)$ is equal to :
$f(x)=e^x \sin x$, then $f^{(6)}(x)$ is equal to :
- $e^{6 x} \sin 6 x$
- $-8 e^x \cos x$
- $8 e^x \sin x$
- $8 e^x \cos x$
Solution
$f(x)=e^x \sin x$
$\therefore f^{\prime}(x)=e^x \cos x+\sin x e^x$
$\Rightarrow f^{\prime \prime}(x)=e^x \cos x-e^x \sin x+e^x \sin x$ $+e^x \cos x$
$=2 e^x \cos x$
Now, $\quad f^{\prime \prime \prime}(x)=-2 e^x \sin x+2 e^x \cos x$
and $\quad f^{i v}(x)=-2 e^x \sin x-2 e^x \cos x$ $+2 e^x \cos x-2 e^x \sin x$
$=-4 e^x \sin x$
$f^v(x)=-4 e^x \cos x-4 e^x \sin x$
$f^{v i}(x)=-4 e^x \cos x+4 e^x \sin x+4 e^x \sin x$-4 e^x \cos x$
$=-8 e^x \cos x$
Asked in: AP EAMCET 2006
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