Question

Rút Gọn 

\(\left(x-1\right)\left(x+1\right)-x\left(x+3\right)\)

Answer 1

\(\left(x-1\right)\left(x+1\right)-x\left(x+3\right)\)

\(=\left(x^2-1\right)-\left(x^2+3x\right)\)

\(=x^2-1-x^2-3x\)

\(=\left(x^2-x^2\right)-3x-1\)

\(=-3x-1\)

Answer 2

`!`

`(x-1)(x+1)-x(x+3)`

`= x^2+x-x-1-(x^2+3x)`

`= x^2 -1-x^2+3x`

`= 3x-1`