Question

Giúp mình bài 3 trong hình với

Answer 1

\(\left(x-2\right)\left(x+2\right)-\left(x+1\right)^2+\left(x-1\right)\left(x+2\right)\\ =x^2-4-\left(x^2+2x+1\right)+\left(x^2-x-2\right)\\ =x^2-4-x^2-2x-1+x^2+x-2\\ =x^2-x-7\)

Thay x=2 ta có:

\(x^2-x-7\\ =4-2-7\\ =-5\)

Answer 2

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

<=> \(\left[{}\begin{matrix}2x-3=0\\2x+3=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\x=\dfrac{-3}{2}\end{matrix}\right.\)