solving equations by factoring

[Tresa332006]

My problem is x^2 -9x =-20

Ok here's how I worked it;

x^2 - 9x - 20 = 0
x^2 - 5x - 4x - 20

x^2 - 5x - 4x - 20 is my answer

I would like to know if I left out any steps or is this right?

 

[Gene]

You show some signs of starting, but you havn't factored anything. When you factor
x²... you get
(x+a)(x+b)=x²+(a+b)x+ab
x^2 -9x +20 = 0
The +20 says either both are positive or both are negative. The -9 says at least one of a & b is negative. You have found that
(a+b)x = -9x = -(4+5)x and luckly(?) 4*5=ab=20 so the factors are
(x-4)(x-5) = 0
To solve the equation you note that either (x-4) = 0 or (x-5) = 0
The solution is x=4 or 5.

Edited to correct b² to ab

 

[Tresaj332006]

Thanks for the help I guess I will have to start all over. Thanks for letting me know.