Integrate me

Calculus Level pending

0 1.5 e x s i n ( 2 x ) d x \int _{ 0 }^{ 1.5 }{ { e }^{ x }sin(2x)dx }


The answer is 2.30123.

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1 solution

Chew-Seong Cheong
Jul 29, 2015

Using integration by parts, we have:

0 1.5 e x sin ( 2 x ) d x = [ e x cos 2 x 2 ] 0 1.5 + 1 2 0 1.5 e x cos ( 2 x ) d x = e 1.5 cos 3 2 + 1 + [ e x sin 2 x 4 ] 0 1.5 1 4 0 1.5 e x sin ( 2 x ) d x 5 4 0 1.5 e x sin ( 2 x ) d x = e 1.5 cos 3 2 + 1 + e 1.5 sin 3 4 0 0 1.5 e x sin ( 2 x ) d x = 4 + e 1.5 ( sin 3 2 cos 3 ) 5 = 2.301 \begin{aligned} \int_0^{1.5} {e^x \sin{(2x)}} dx & =\left[ - \frac{e^x \cos{2x}}{2} \right]_0^{1.5} + \frac{1}{2} \int_0^{1.5} {e^x \cos{(2x)}} dx \\ & = \ -\frac{e^{1.5} \cos{3}}{2} + 1 + \left[\frac{e^x \sin{2x}}{4} \right]_0^{1.5} \\ & \quad \quad - \frac{1}{4}\int_0^{1.5} {e^x \sin{(2x)}} dx \\ \Rightarrow \frac{5}{4} \int_0^{1.5} {e^x \sin{(2x)}} dx & = -\frac{e^{1.5} \cos{3}}{2} + 1 + \frac{e^{1.5} \sin{3}}{4} - 0 \\ \Rightarrow \int_0^{1.5} {e^x \sin{(2x)}} dx & = \frac{4 + e^{1.5}( \sin{3} - 2\cos{3})}{5} = \boxed{2.301} \end{aligned}

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