Question

A=(x-1)^2-2(x-1)(x+2)+(2+x)^2

Answer 1

\(A=\left(x-1\right)^2-2\left(x-1\right)\left(x+2\right)+\left(2+x\right)^2\)

Hằng đẳng thức áp dụng : \(a^2-2ab+b^2=\left(a-b\right)^2\)

\(\Rightarrow A=\left[\left(x-1\right)-\left(x+2\right)\right]^2\)

\(\Rightarrow A=\left(x-1-x-2\right)^2\)

\(\Rightarrow A=\left[\left(x-x\right)+\left(-2-1\right)\right]^2\)

\(\Rightarrow A=\left(-3\right)^2\)

\(\Rightarrow A=9\)

Vậy A = 9

Answer 2

A=(x-1-x-2)^2=(-3)^2=9

Answer 3

Ta có:

\(A=\left(x-1\right)^2-2\left(x-1\right)\left(x+2\right)+\left(2+x\right)^2\\ =\left(x-1\right)^2-2\left(x-1\right)\left(x+2\right)+\left(x+2\right)^2\\ =\left[\left(x-1\right)-\left(x+2\right)\right]^2\\ =\left(x-1-x-2\right)^2\\ =\left(-3\right)^2=9\)

Vậy \(A=9\)

*HĐT số 2: \(\left(a-b\right)^2=a^2-2ab+b^2\)