Question

[Học toán ngu ngu ấy mà]

Bài 1.Rút gọn biểu thức

a) (a+b)^2 - (a-b)^2

b) (a+b)^3 - (a-b) - (2b)^3

Answer 1

[Sincere]

\(a,\left(a+b\right)^2-\left(a-b\right)^2\)

\(=a^2+2ab+b^2-a^2+2ab-b^2\)

\(=4ab\)

\(b,\left(a+b\right)^3-\left(a-b\right)-\left(2b\right)^3\)

\(=a^3+3a^2b+3ab^2+b^3-a+b-8b^3\)

Answer 2

[Hồ Anh Thông]

a) \(\left(a+b\right)^2-\left(a-b\right)^2\)

      \(\left(a+b-a+b\right)\left(a+b+a-b\right)\)

     \(\left(2b\right)\left(2a\right)\)

     \(4ab\)

b) \(\left(a+b\right)^3-\left(a-b\right)-\left(2b\right)^3\)

    \(a^3+3a^2b+3ab^2+b^3-a+b-8b^3\)

    \(a\left(a^2-1\right)+3\left(a^2b+ab^2\right)+b\left(b^2+1-8b^2\right)\)

   \(a\left(a-1\right)\left(a+1\right)+3\left[ab\left(a+b\right)\right]+b\left(-7b^2+1\right)\)