Question 77691
You can approximate the equation by looking at its roots


For instance, this graph


{{{ graph( 300, 200, -6, 5, -10, 10, (x+5)(x-3)) }}}


has roots of x=-5 and x=3. So for any root of x=a, the factor will be 


{{{x-a=0}}}. So if we have roots of x=a and x=b, then our factorization is:

{{{(x-a)(x-b)=0}}}  

So this means our factorization is {{{(x+5)(x-3)}}} since we have roots of x=-5 and x=3

Now we just foil {{{(x+5)(x-3)}}} to get {{{x^2+2x-15}}}. This doesn't work all the time since we might have a stretch or compression factor.