(х+1)² - 16 = (х+1)² - 4² = (x + 1 - 4)(x + 1 + 4) = (x - 3)(x + 5)
a² -12a + 36 = a² -2·6·a + 6² = (a - 6)²
16m² +24mn + 9n² = (4m)² +2·4m·3n + (3n)² = (4m + 3n)²