\(\left(x-2\right)\left(x+2\right)-\left(x+1\right)^2+\left(x-1\right)\left(x+2\right)\\ =x^2-4-\left(x^2+2x+1\right)+\left(x^2-x-2\right)\\ =x^2-4-x^2-2x-1+x^2+x-2\\ =x^2-x-7\)
Thay x=2 ta có:
\(x^2-x-7\\ =4-2-7\\ =-5\)
Bài 1:
a. x2 - 2xy + y2 - 1
= (x - y)2 - 12
= (x - y + 1)(x - y - 1)
b. x2 - 8x - 9
= x2 + x - 9x - 9
= x(x + 1) - 9(x + 1)
= (x - 9)(x + 1)
bài 2:
a. 4x2 - 9 = 0
<=> (2x)2 - 32 = 0
<=> (2x - 3)(2x + 3) = 0
<=> \(\left[{}\begin{matrix}2x-3=0\\2x+3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=\dfrac{-3}{2}\end{matrix}\right.\)
