Question 840519
Is your equation {{{f(x)=-(3/4)x^2+15x-77}}}??
You need to complete the square.
{{{f(x)=-(3/4)(x^2-(4/3)15x^2)-77}}}
{{{f(x)=-(3/4)(x^2-20x^2)-77}}}
{{{f(x)=-(3/4)(x^2-20x^2+100)-77+(3/4)(100)}}}
{{{f(x)=-(3/4)(x-10)^2-77+75}}}
{{{highlight(f(x)=-(3/4)(x-10)^2+2)}}}