x^2 + ax + b = (x + c) (x + d)

how do you get c and d from a and b?

Question

x^2 + ax + b = (x + c) (x + d)

how do you get c and d from a and b?

tkhunny · Answer

Why not go the other way?

b = c*d
a = ???

anonymous · Answer

I'm trying to understand factoring and we've been starting fro x^2 + ax + b = 0

tkhunny · Answer

Well, it does not hurt to work backwards.  Very often, this leads to greater understanding.

 (x + c) (x + d)  = x^2 + (c+d)x + cd

Thus a = c+d and b = c*d.  These are very important relationships.

You must find FACTORS of b that will SUM to a.  This is the heart of factoring.

anonymous · Answer

thank you! exactly what I was looking for. that really helps.