What was your question?\(\displaystyle F(x)= \displaystyle{\int^a_b \frac{1}{3}x^3 dx}\)
The left hand side is a function of x, while the rhs is a function of a and b which results in a constant. Is that what you wanted? After all, you never did ask a question!\(\displaystyle F(x)= \displaystyle{\int^a_b \frac{1}{3}x^3 dx}\)