K = (3x+2)²-(3x+2)(x+7)
=(3x+2)(3x+2)-(x+7)
=(3x+2)(3x+2-x-7)
=(3x+2)(2x-5)
L = (5x+3)²-(5x+3)(2x-4)
=(5x+3)(5x+3)-(2x-4)
=(5x+3)(5x+3-2x+4)
=(5x+3)(3x+7)
M = (3x+2)(4x+1)-(4x+1)²
=(4x+1)(3x+2)-(4x+1)
=(4x+1)(3x+2-4x-1)
=(4x+1)(-x+1)
N = (x+3)²+(x+3)
=(x+3)(x+3)+1
=(x+3)(x+4)