Х²+12х+20 = х²+2*6*х+20 = х²+12х+20+16-16 = (х+6)² - 16
x²+12x+36 = (х+6)²
х²+х-2 = х²+2х-х-2 = х²+2*1*х-х-2 = х²+2х+1-1-х-2 = (х+1)² - х - 3
x²+2x+1 = (х+1)²
х²-3х-10 = х²-4х+х-10 = х²-2*2*х+х-10 = х²-4х+4-4+х-10 = (х-2)² + х - 14
x²-4x+4 = (х-2)²
х²-2х-35 = х²-2*1*х+20 = х²-2х-35+1-1 = (х-1)² - 36
x²-2x+1 = (х-1)²