All right, I know that partial derv. are not all that hard. All you do in lets say f(x)= x^2+2yx+3y is find the dervitives of x while you treat y as a constent, and vice versa. But I keep running into problems having square roots. I hat these things. One example could be f(x)= sqr(20-x^2-7y^2). I know yo treat the y as a constent, but I am horrible with my derv. Any help would be appreciated.