Annual Integral!

Calculus Level 3

Evaluate

2016 2017 ( x 2016 2015 2016 x 1 2015 ) 2015 d x \large \int_{2016}^{2017} \left( x^{\frac{2016}{2015}} - 2016 x^{\frac{1}{2015}} \right)^{2015}dx

2017 2018 \frac{2017}{2018} 2017 2016 \frac{2017}{2016} 2018 2017 \frac{2018}{2017} 2016 2017 \frac{2016}{2017}

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2 solutions

I = 2016 2017 ( x 2016 2015 2016 x 1 2015 ) 2015 d x = 2016 2017 x ( x 2016 ) 2015 d x Let u = x 2016 d u = d x = 0 1 ( u + 2016 ) u 2015 d u = 0 1 ( u 2016 + 2016 u 2015 ) d u = 1 2017 + 1 = 2018 2017 \begin{aligned} I & = \int_{2016}^{2017} \left(x^{\frac {2016}{2015}}-2016x^{\frac 1{2015}}\right)^{2015} dx \\ & = \int_{2016}^{2017} x(x-2016)^{2015} dx & \small \color{#3D99F6} \text{Let }u=x-2016 \implies du = dx \\ & = \int_0^1 (u+2016)u^{2015} du \\ & = \int_0^1 \left(u^{2016}+2016u^{2015}\right) du \\ & = \frac 1{2017} + 1 = \boxed{\dfrac {2018}{2017}} \end{aligned}

X X
Jul 3, 2018

2016 2017 ( x 2016 2015 2016 x 1 2015 ) 2015 d x \displaystyle\int_{2016}^{2017} \left( x^{\frac{2016}{2015}}- 2016 x^{\frac{1}{2015}} \right)^{2015}dx

= 2016 2017 ( ( x 2016 ) x 1 2015 ) 2015 d x \displaystyle=\int_{2016}^{2017}\left( (x-2016)x^{\frac1{2015}} \right)^{2015} dx

= 2016 2017 ( x 2016 ) 2015 x d x \displaystyle=\int_{2016}^{2017} (x-2016)^{2015}x dx

= 0 1 u 2015 ( u + 2016 ) d u \displaystyle=\int_0^1 u^{2015}(u+2016) du ( x = u + 2016 , d x = d u x=u+2016,dx=du )

= 0 1 u 2016 + 2016 u 2015 d u \displaystyle=\int_0^1 u^{2016}+2016u^{2015}du

= 1 2017 + 1 = 2018 2017 \displaystyle=\frac1{2017}+1=\frac{2018}{2017}

Please mention the substitution you've done in step 4 with change in variable to avoid confusion.

Tapas Mazumdar - 2 years, 11 months ago

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OK,done editting.

X X - 2 years, 11 months ago

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