Hello Everyone, I'm trying to do this question: Find a function f such that f'(x)=x^3 and the line x+y=0 is tangent to the graph of f. Now to find the general equation of f(x) all you have to do is take the extremely basic integral of F'(x) which is going to be f(x) = x^4/4 +C. Now the question asks you to find the equation so that f'(x) and x+y=0 is tangent to this equation. I really have no idea how to go about doing thing to be honest. At first I thought that maybe you could set f'x equal to x+y =0 solve, and then set the answer equal to f(x) but I did this and my answer was horrible wrong. Any suggestions on how to go about this question?