Integral 22

Calculus Level 3

0 1 x x x . . . d x \displaystyle {\huge \int_{0}^{1}} \displaystyle \sqrt{\dfrac{x}{\sqrt{\dfrac{x}{\sqrt{\dfrac{x}{\sqrt{}...}}}}}} \, dx

If the above integral is the form of a b \dfrac ab , where a a and b b are coprime positive integers, find a + b a+b .


The answer is 7.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

Rishabh Jain
Mar 19, 2016

y = x 1 2 1 4 + 1 8 + Infinite GP \Large y=x^{\overbrace{\small{\frac{1}{2}-\frac{1}{4}+\frac{1}{8}+\cdots}}^{\color{#D61F06}{\text{Infinite GP}}}}

= x 1 2 1 + 1 2 = x 1 3 \Large =x^{\small{\frac{\frac 12}{1+\frac 12}}}=x^{\frac 13}

Hence we have to find 0 1 x 1 3 d x \int_{0}^1 x^{\frac 13}\,dx . 0 1 x 1 3 d x \Large{ \int_0^1x^{\frac 13}\,dx} = 3 4 x 4 3 0 1 = 3 4 \Large{=\dfrac{3}{4} x^{\frac 43}|_{0}^1=\dfrac 34 } 3 + 4 = 7 \huge \therefore ~3+4=\boxed 7

i did same

Dev Sharma - 5 years, 2 months ago

Same here (+1)

Noel Lo - 3 years, 11 months ago

Log in to reply

Great... :-)

Rishabh Jain - 3 years, 11 months ago
William Allen
Apr 15, 2019

t = x x x x = t 3 d x = 3 t 2 d t t=\sqrt{\frac{x}{\sqrt{\frac{x}{\sqrt{\frac{x}{\ddots}}}}}} \implies x=t^{3} \implies dx=3t^{2}dt 0 1 3 t 3 d t = [ 3 t 4 4 ] 0 1 = 3 4 3 + 4 = 7 \int_{0}^{1}{3t^3}dt = \left [\frac{3t^4}{4} \right ]_{0}^{1} = \frac{3}{4} \\ 3+4=\boxed{7}

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...