a)4x² + 4x+1
=(2x)²+2.2x.1+1²
=(2x+1)²
b)(6x+3)-(2x-5)(2x+1)
=3(2x+1)-(2x-5)(2x+1)
=-2(2x+1)(x+1)
c)(5x+4)²-49x²
=(5x+4-7)(5x+4+7)
=(5x-3)(5x+11)
d)$x^{4}$ + 2x³ - 15y² + 6z
=x³(x+2)-x(x+2)
=x(x²-1)(x+2)
=x(x-1)(x+1)(x+2)
e)15xy³ - 2yz - 15y² + 6z=(câu này mk ko bt làm)
f)9(2x+3)² - 4(x+1)²=9(4x²+12x+9) - 4(x²+2x+1)
=36x²+108x+81-4x²-8x-4
=32x²+100x + 77
=(32x² + 44x) + (56x + 77)
=4x(8x+11)+7(8x+11)
=(4x+7)(8x+11)