Varnish HTTP Cache (Poul-Henning Kamp Talk)
vimeo.com4 pointsby bkz0 comments
x^2 = x^2
x^2 + (r^2 - r^2) = x^2
(x^2 - r^2) + r^2 = x^2
(x + r)(x - r) + r^2 = x^2 (x + r)(x - r) = x^2 - r^2
Which is useful if you need to calculate the opposite where two numbers are mirrored around a suitable even number, i.e. 28 * 32 -> (30 + 2)(30 - 2) = 30^2 - 2^2