Đáp án:
Giải thích các bước giải:
a) $(2x-3)^3+(4x+1)(16x^2+4x+1)$
$=8x^3-36x^2+54x-27+64x^3+16x^2+4x+16x^2+4x+1$
$=(8x^3+64x^3)+(-36x^2+16x^2+16x^2)+(54x+4x+4x)+(-27+1)$
$=72x^3-4x^2+62x-26$
b) $(x-2)(x^2+2x+4)-(x-y)^2$
$=x^3-8-(x^2-2xy+y^2)$
$=x^3-x^2+2xy-y^2-8$
c) $(3x+y)^3-(x+2y)(x^2-2xy+4y^2)$
$=27x^3+27x^2y+9xy^2+y^3-(x^3+8y^3)$
$=27x^3+27x^2y+9xy^2+y^3-x^3-8y^3$
$=26x^3+27x^2y+9xy^2-7y^3$
d) $(3x-2y)(x+y)+(y+3x)^3$
$=3x^2+3xy-2xy-2y^2+y^3+9xy^2+27x^2y+27x^3$
$=3x^2+xy-2y^2+y^3+9xy^2+27x^2y+27x^3$
Thay:
a) Thay $x=-2$
$72.(-2)^3-4.(-2)^2+62.(-2)-26$
$=72.(-8)-4.(-4)+62.(-2)-26$
$=-576+16-124-26$
$=710$
b)Thay $x=1;y=\frac{-1}{2}$
$1^3-1^2+2.1.\frac{-1}{2}-(\frac{-1}{2})^2-8$
$=1-1-1-\frac{1}{4}-8$
$=\frac{-37}{4}$
c) Thay $x=1;y=2$
$26.1^3+27.1^2.2+9.1.2^2-7.2^3$
$=26+54+36-56$
$=60$
d) Thay $x=\frac{1}{3};y=-2$
$3.(\frac{1}{3})^2+(\frac{1}{3}).-2-2(-2)^2+(-2)^3+9.(\frac{1}{3}).(-2)^2+27.\frac{1}{3}^2.(-2)+27\frac{1}{3}^3$
$=\frac{1}{9}+\frac{-2}{3}-8-8+12+3$
$=\frac{-14}{9}$
Học tốt!!!
