Thu gọn đa thức sau: (7x 2 -x-1)(x-5)+(4 x2+3)(5-2x)
2 câu trả lời
(7x2-x-1)(x-5)+(4x2+3)(5-2x)
=x(7x2-x-1)-5(7x2-x-1)+5(4x2+3)-2x(4x2+3)
=7x3-x2-x-35x2+5x+5+20x2+15-8x3-6x
=(7x3-8x3)+(20x2-35x2-x2)+(5x-6x-x)+(5+15)
=-x3-16x2-2x+20
(7x2-x-1)(x-5)+(4x2+3)(5-2x)
=x(7x2-x-1)-5(7x2-x-1)+5(4x2+3)-2x(4x2+3)
=7x3-x2-x-35x2+5x+5+20x2+15-8x3-6x
=(7x3-8x3)+(20x2-35x2-x2)+(5x-6x-x)+(5+15)
=-x3-16x2-2x+20