p2 - 8p = 0
The square would be (8/2)2 = 42 = 16
So, p2 - 8p + 16 = 16
then (p - 4)2 = 42
So that (p - 4) = +/- 4
then p = 4 +/- 4
ie p = 8 or p = 0
With this particular question, factorisation is so much
easier:
p2 - 8p = 0
p(p - 8) = 0
So p = 0 or p = 8
Done!