Hi, i am trying to find the arc length of a curve over y=x^(2/3) from x=1 to x=8. I know that in order to use the length equation i have to find 1+[f '(x)]^2 which equals 1+(4/9)x^(-2/3). The next step in my book turns that into (9x^(2/3)+4)/(9x(2/3)). I cant figure out why they did that, can anyone help me.

thanks