 Problem Statement
 I cannot deal with this integration. ##\int\sqrt{1+y^2}##
 Relevant Equations

##\int\sqrt{1+y^2}##
##tan\theta=3y##
This is the integral I try to take. ##\int\sqrt{1+9y^2}## and ##9y^2=tan^2\theta## so the integral becomes ##\int\sqrt{1+tan^2\theta}=\sqrt {sec^2\theta}##. Now I willl calculate dy.
## tan\theta=3y ## and ##y=\frac {tan\theta}3## and ##dy=\frac{1+tan^2\theta}3##
Here is where I can only reach. I can't go any further.
Thanks.
## tan\theta=3y ## and ##y=\frac {tan\theta}3## and ##dy=\frac{1+tan^2\theta}3##
Here is where I can only reach. I can't go any further.
Thanks.