Solve the integral

Calculus Level 3

1 e x sin ( ln x ) d x = ? \large \int_1^e \dfrac{\partial}{\partial x} \sin(\ln|x|) \ dx=\ ?


The answer is 0.841471.

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3 solutions

Chew-Seong Cheong
Jun 27, 2018

1 e x sin ( ln x ) d x = sin ( ln x ) 0 e = sin ( ln e ) sin ( ln 1 ) = sin 1 sin 0 = sin 1 0.841 \int_1^e \frac \partial {\partial x}\sin (\ln |x|) \ dx = \sin (\ln|x|) \ \bigg|_0^e = \sin (\ln e) - \sin (\ln 1) = \sin 1 - \sin 0 = \sin 1 \approx \boxed{0.841}

Guilherme Franco
Jun 26, 2018

First of all, you can cancel this derivative with the integration, and just apply the limits into the derivativent. sin ( ln e ) sin ( ln 1 ) = sin 1 sin 0 \sin(\ln e)-\sin(\ln 1) = \sin 1 - \sin 0 , then you calculate the results sin 1 0.841471 \sin 1 \approx 0.841471 .

Tsungyen Tsai
Jun 29, 2018

If f = f ( x ) \displaystyle f=f(x) , then d f = f x d x \displaystyle df=\frac{\partial f}{\partial x} dx .

Hence, 1 e x sin ( ln x ) d x = 1 e d ( sin ( ln x ) ) \displaystyle \int_1^{e} \frac{\partial }{\partial x}\sin{(\ln{|x|})} dx =\int_1^{e} d \left(\sin{(\ln{|x|})}\right)

According to FTOC II, we finally obtain

1 e x sin ( ln x ) d x = 1 e d ( sin ( ln x ) ) = sin ( ln e ) sin ( ln 1 ) = sin 1 0.841 \displaystyle \int_1^{e} \frac{\partial }{\partial x}\sin{(\ln{|x|})} dx =\int_1^{e} d \left(\sin{(\ln{|x|})}\right) = \sin{(\ln{|e|})} - \sin{(\ln{|1|})} = \sin{1}\approx 0.841

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