# Math Help - Factoring by Grouping

1. ## Factoring by Grouping

note: x^2 means x ( or whatever variable) to the power of 2
p^2-q^2+r^2-2pr

factor by grouping ( or any other method)
i've tried to factor it into this format: (x-y+z)(x-y-z), but i can't seem to do it. the answer key says that the answer is (p-r+q)(p-r-q), but I don't understand how they got to it.

2. Hello, mmsan!

Factor: . $p^2 - q^2 + r^2 -2pr$

It's a sneaky one . . .

Group it like this: . $(p^2 - 2pr + r^2) - q^2$

Factor: . $(p - r)^2 - q^2\;\;\Leftarrow$
difference of squares!

Factor again: . $[(p - r) - q][(p - r) + q] \;=\;(p - r - q)(p - r + q)$