Hello, mmsan!
Factor: .
It's a sneaky one . . .
Group it like this: .
Factor: . difference of squares!
Factor again: .
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.