Question 19850
Did you really mean..."Find x such that f(x) = 3" ??

If {{{f(x) = 13x^2+65x+3}}}, then:
{{{f(x) = 3}}} = {{{13x^2 + 65x + 3 = 3}}} Solve for x.
{{{13x^2 + 65x + 3 = 3}}} Subtract 3 from both sides of the equation.
{{{13x^2 + 65x = 0}}} Factor 13x from the left side.
{{{13x(x + 5) = 0}}} Apply the zero products principle.
{{{13x = 0}}} and/or {{{x + 5 = 0}}}
If {{{13x = 0}}} then, x = 0
If {{{x + 5 = 0}}} then, {{{x = -5}}}

Check:

{{{f(0) = 13(0)^2 + 65(0) + 3}}} = {{{3}}}
{{{f(-5) = 13(-5)^2 + 65(-5) + 3}}} = {{{325 + (-325) + 3 = 3}}}