bài 1 :
a) x^3(x^2 + 3x – 5)
=x^5+3x^4-5x^3
b) (xy – 2).(x^3 – 2x – 6)
= x^4y - 2x^2y - 6xy - 2x^3 + 4x + 12
c)(5x^3 – x^2 + 2x – 3).(4x^2 – x + 2)
= 20x^5 - 4x^4 + 8x^3 - 12x^2 -5x^4 + x^3 -2x^2 + 3x + 10x^3 - 2x^2 + 4x - 6
=20x^5 -9x^4 +19x^3 -16x^2 -6
bài 2:
a) (2x – 2y)^2 = 4x^2 - 8xy + 4y^2
b) (x^2 +3)^2 = x^4 + 6x^2 + 9
c) (x – 2)(x^2 + 2x + 4)= x^3 - 8
d) (2x – 1)^3 = 8x^3 - 12x^2 + 6x - 1
bài 3:
a) (x – 2)^2 – (x – 3)(x + 3) = 6
=> x^2 - 4x + 4 - x^2 + 9 = 6
=> -4x = -7
=> x= 7/4
b) (x – 3)^2 – (x – 1)(x + 1) = 10
=> x^2 - 6x + 9 - x^2 +1 = 10
=> -6x = 0
=>x=0