Fundamental Theorem of Calculus Integration I've been trying to work on this problem for an hour and for some reason I'm apparently not inputting the correct answer. The problem was to find the derivative of $\int_{x^5}^{x^7} (2t-1)^3 dt$ and I used F.T.O.C to get $-(2x^5-1)^3+(2x^7-1)^3$, but it keeps saying it wasn't correct, all I did was separate the problem into 2 bounds from $x^5$ to 0 and 0 to $x^7$ and reversed the $x^5$ to 0 one making it negative like F.T.O.C guides. What am I doing wrong and what is the correct answer?

let us use the fact that $d \left(\int_a^b f(t) dt \right)= f(b)db - f(a) da$ to do 
$$d\int_{x^5}^{x^7}(2t-1)^3\, dt = (2x^7-1)^3 dx^7 -(2x^5-1)^3dx^5 =(2x^7-1)^3 7x^6 \, dx -(2x^5-1)^3 5x^4 \,dx$$ if you divide it out, you get 
$$\frac{d}{dx}\int_{x^5}^{x^7}(2t-1)^3\, dt = 7x^6(2x^7-1)^3   -5x^4(2x^5-1)^3 $$
