Áp dụng hằng đẳng thức
1. (x+2y)2 = x2 +2.x.2y + (2y)2
= x2 + 4xy + 4y2
2. (2x + 3y)2 = 4x2 + 12xy + 9y2
3. (3y - 2y)2 = 9x2 - 12xy + 4y2
4. (5x - y)2 = 25x2 - 10xy + y2
5. (x + 1/4)2 = x2 + 1/2x + 1/16
6. (2x - 1/2)2 = 4x2 - 2x + 1/4
7. (1/3x - 1/2y)2 = 1/9x2 - 1/3xy + 1/4 y2
8. (3x + 1) (3x-1) = 9x2 - 1
9. (x2 + 2/5y) (x2 - 2/5y)
= (x2)2 - (2/5y)2
= x4 - 4/25y
10. (x/2 - y) (x/2 + y) = x2/4 - y2
11. (x/2 - 2y)2 =x2/4−2xy + 4y2
12. \((\sqrt{2x} - y^)\)2 = 2x - 2y \(\sqrt{2x} +y^{2}\)
13. (3/2x + 3y)2 =9x2/4 + 9xy + 9y2
Bài toán 2:
1. (x + 1/3)2 = x2+2x/3 +1/9
2. (2x + y2)3 = y6 + 6xy4 +12x2y2 + 8x3