Evaluate `intsqrt(1+y^2)*2ydy`

Explanation

Let `I=intsqrt(1+y^2)*2ydy`
Let `u=1+y^2`, then `du=2ydy`.
`I=intu^(1//2)du`
`=(u^((1//2)+1))/((1//2)+1)` [Integrate, using rule no. 3 with `n=1//2`]
`=2/3u^(3//2)+C` [Simpler form]
`2/3(1+y^2)^(3//2)+C` [Replace u by `1+y^2`]