# Method of Substitution

• April 1st 2009, 05:44 AM
robdarftw
Method of Substitution
y=x^3-x^2-1
y=x^2+15x-1
i completely forgot how to do this. i know method of elimination, but it says i gotta use substitution. any ideas?
• April 1st 2009, 08:47 AM
red_dog
Substitute y from the first equation in the second equation:

$x^3-x^2-1=x^2+15x-1\Rightarrow x^3-2x^2-15x=0\Rightarrow x(x^2-2x-15)=0$

Then $x=0$ or $x^2-2x-15=0$

Now solve the quadratic, then replace x and find y.