x 2 \displaystyle{x^2} Laid Down On The Floor

Calculus Level 4

1 2 ( x x 2 + x 2 x ) d x \large \int_{1}^{2} \left(x^{\lfloor x^2 \rfloor} + {\lfloor x^2 \rfloor}^{x} \right) \, dx

The integral above can be expressed as a b + c + d e + 2 f 2 g ln h + i 3 j ln k . \dfrac{a}{b} + \sqrt{c} + \dfrac{\sqrt{d}}{e} + \dfrac{2^{\sqrt{f}}-2^{\sqrt{g}}}{\ln h } + \dfrac{i - 3^{\sqrt{j}}}{ \ln k}. What is the sum of all of these constants from a \displaystyle{a} to k ? \displaystyle{k}?

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The answer is 39.

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2 solutions

Pranjal Jain
Nov 14, 2014

1 2 x x 2 + x 2 x d x \displaystyle\int_{1}^{2} x^{\lfloor x^{2} \rfloor}+\lfloor x^{2} \rfloor^{x} dx

1 2 x x 2 + x 2 x d x + 2 3 x x 2 + x 2 x d x + 3 2 x x 2 + x 2 x d x \displaystyle\int_{1}^{\sqrt{2}} x^{\lfloor x^{2} \rfloor}+\lfloor x^{2} \rfloor^{x} dx+\displaystyle\int_{\sqrt{2}}^{\sqrt{3}} x^{\lfloor x^{2} \rfloor}+\lfloor x^{2} \rfloor^{x} dx+\displaystyle\int_{\sqrt{3}}^{2} x^{\lfloor x^{2} \rfloor}+\lfloor x^{2} \rfloor^{x} dx

= 1 2 ( x + 1 ) d x + 2 3 ( x 2 + 2 x ) d x + 3 2 x 3 + 3 x d x =\displaystyle\int_{1}^{\sqrt{2}} (x+1) dx+\displaystyle\int_{\sqrt{2}}^{\sqrt{3}} (x^{2}+2^{x}) dx+\displaystyle\int_{\sqrt{3}}^{2} x^{3}+3^{x} dx

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

= 2 3 + 3 + 2 3 2 2 l n 2 + 9 3 3 l n 3 + 5 4 =\frac{\sqrt{2}}{3}+\sqrt{3}+\frac{2^{\sqrt{3}}-2^{\sqrt{2}}}{ln 2}+\frac{9-3^{\sqrt{3}}}{ln 3}+\frac{5}{4}

Hence answer is 5+4+3+2+3+3+2+2+9+3+3= 39 \boxed{39}

Maybe I'm being stupid, and i know i am, but don't skip 'dx' while writing integrals where you want to integrate w.r.t. x. But i appreciate your effort in writing that solution, because i myself find it hard to write such solutions in LaTeX ;)

Aakarshit Uppal - 6 years, 4 months ago

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You're not at all being stupid. In fact, without the d x \mathrm dx 's, his solution is meaningless (in mathematical contexts).

@Pranjal Jain , care to edit your solution?

Prasun Biswas - 5 years, 11 months ago

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Oops! Thanks for notifying! I'll fix this.

Pranjal Jain - 5 years, 11 months ago
Sudhanshu Dalela
Nov 13, 2014

Integrate (x+1) from 1 to root 2 + Integrate (x^2 + 2^x) from root 2 to root 3 + Integrate (x^3 + 3^x) from root 3 to 2 Simplify & add Answer is 39

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