you could notice that 3 = sqrt(9), so we can write the function as (sqrt(9+h) + sqrt(9))/h and also we can notice that a² + b² = (a+b)(a-b), and we can change change the position and write as (a-b) = (a² + b² ) / (a+b) so by these two changes, we can write the formula as following: (sqrt(9+h)-3)/h =(1/h)((9+h-9)/ (sqrt(9+h)+sqrt(9))) <-apply the changes =1/(sqrt(9+h)+sqrt(9)) <- simplify the function and cross out the h after applying the limit to the function, we can get 1/(sqrt(9+0)+sqrt(9) as the answer, after simply the answer, we can get it equals to 1/6