(4Đ) A) (2Đ) CHỨNG MINH
Câu2:(4đ)
a) (2đ) Chứng minh: Nếu a + b + c = 0 thì a
3
+ b
3
+ c
3
= 3abc
áp dụng ta có: (3x – 2)
3
– (x – 3)
3
– (2x + 1)
3
= (3x – 2)
3
+ ( - x + 3)
3
+ ( - 2x - 1)
3
= 3(3x – 2)( - x + 3)( - 2x – 1).
b) (2đ) Ta có: (3x – 2)
3
– (x – 3)
3
= (2x + 1)
3
⇔ (3x – 2)
3
– (x – 3)
3
- (2x + 1)
3