Floor under integration again

Calculus Level 4

100 0 1.5 x x 2 d x = ? \large 100 \int_{0}^{1.5} x\lfloor x^2 \rfloor \, dx = \ ?


The answer is 75.

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1 solution

Pranjal Jain
Nov 30, 2014

0 1.5 x x 2 d x \displaystyle\int_{0}^{1.5} x\lfloor x^{2} \rfloor dx = 0 1 x x 2 d x + 1 2 x x 2 d x + 2 1.5 x x 2 d x =\displaystyle\int_{0}^{1} x\lfloor x^{2} \rfloor dx+\displaystyle\int_{1}^{\sqrt{2}} x\lfloor x^{2} \rfloor dx+\displaystyle\int_{\sqrt{2}}^{1.5} x\lfloor x^{2} \rfloor dx = 0 1 ( x × 0 ) d x + 1 2 ( x × 1 ) d x + 2 1.5 ( x × 2 ) d x =\displaystyle\int_{0}^{1} (x×0) dx+\displaystyle\int_{1}^{\sqrt{2}} (x×1) dx+\displaystyle\int_{\sqrt{2}}^{1.5} (x×2) dx

= [ x 2 2 ] 1 2 + [ x 2 ] 2 1.5 = 1 2 + 1 4 = 3 4 =\bigg [\frac{x^{2}}{2} \bigg ]_{1}^{\sqrt{2}} + \bigg [x^{2} \bigg ]_{\sqrt{2}}^{1.5}=\frac{1}{2}+\frac{1}{4}=\frac{3}{4}

So answer is 100 × 3 4 = 75 100×\frac{3}{4}=\boxed{75}

thanks for posting the solution.Nice solution.

Sandeep Bhardwaj - 6 years, 6 months ago

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Most welcome! You keep on posting nice questions and Ill try to answer them all the same way!

Pranjal Jain - 6 years, 6 months ago

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