A quadratic function f(x) is hidden from view. You must find all intervals where f(x) is increasing. Choose the form of the quadratic function f(x) that you would like to see in order to answer the question most efficiently. Standard: f(x)=-3x^{2}+18x+21
Vertex: f(x)=-3(x-3)^{2}+48
Factored: f(x)=-3(x-7)(x+1)