Bài 2: Tìm x, biết :
a) 9x2 – 49 = 0
b) (x + 3)(x2 – 3x + 9) –x(x – 1)(x + 1) – 27 = 0
c)(x – 1)(x + 2) – x – 2 = 0
d) x(3x + 2) + (x + 1)2 – (2x – 5)(2x + 5) = 0
e) (4x + 1)(x - 2) - (2x -3)(2x + 1) = 7
Bài 3: Rút gọn biểu thức :
a) (2x + 1)2 +(2x + 3)2 – 2(2x + 1)(2x + 3)
b) (2x – 3)(2x + 3) – (x + 5)2 – (x – 1)(x + 2)
c) (x + 2y)(x2 – 2xy + 4y2) – (x – y)(x2 + xy + y2)
d) x2(x + y) + y2(x + y) + 2x2y + 2xy2
e) (x + y)2 + (x – y)2 – 2(x + y)(x - y)
f) (a + b)3 - (a – b)3 – 2b3
g) (x – y)(x + y)(x2 + y2)(x4 + y4)
(Mong mn giúp đỡ)
