It's not clear whether you are talking about CompuChip's x(x-1)= x^{2}- x or matt grimes' sin^{2}x+ cos^{2}x= 1 but you will find the first in any elementary algebra text and the second in any trigonometry text.^ That's odd, I've covered lots of identities and I've never once seen that in any text book (nor during the bajillion trig identities I was forced to prove in highschool.)