## double integrals and midpoint rule

Use midpoint rule for double integral with m=n=2 to estimate area of surface z=xy+x^2+y^2 , 0<= x <= 5 , o <= y <= 5. Round to 3 decimals.

I found Fx and Fy
Fx=2x+y
Fy=2y+x
I put those into a square root and squared each one and added +1
I found the 4 points to be (5/4,5/4),(5/4,15/4),(15/4,5/4),(15/4,15/4) and put those into the square root to get sqrt(466)/4 + sqrt(1866)/4 + sqrt(1866)/4 + sqrt(4066)/4 = 42.9

which is not correct and Im not sure what I have done wrong. I also tried my calculator which gave me 269 which is not correct either.