What is the arclength of f(x)=x-sqrt(e^x-2lnx)f(x)=xex2lnx on x in [1,2]x[1,2]?

1 Answer
Mar 3, 2017

L=int_1^2sqrt(1+(1-(xe^x-2)/(2xsqrt(e^x-2lnx)))^2)dxapprox1.0630L=211+(1xex22xex2lnx)2dx1.0630

Explanation:

The arc length of the curve of ff on x in [a,b]x[a,b] is given by

L=int_a^bsqrt(1+(f'(x))^2)dx

Here, f(x)=x-(e^x-2lnx)^(1/2) so

f'(x)=1-1/2(e^x-2lnx)^(-1/2)(e^x-2/x)

color(white)(f'(x))=1-(xe^x-2)/(2xsqrt(e^x-2lnx))

Then the arc length is given by

L=int_1^2sqrt(1+(1-(xe^x-2)/(2xsqrt(e^x-2lnx)))^2)dxapprox1.0630