(x + 2)(x – 2) – (x – 3)(x + 1)

= x2 – 22 – (x2 + x – 3x – 3)

= x2 – 4 – x2 – x + 3x + 3

= 2x – 1

`Answer:`

`a)`

`A=5(x+1)^2-3(x-3)^2-4(x^2-4)`

`=>A=5(x^2+2x+1)-3(x^2-6x+9)-4x^2+16`

`=>A=5x^2+10x+5-3x^2+18x-27-4x^2+16`

`=>A=(5x^2-3x^2-4x^2)+(10x+18x)+(5-27+16)`

`=>A=-2x^2+28x-6`

`b)`

`B=5(x+1)^2-3(x-3)^2-4(x+2)(x-2)`

`=2x(3x+5)-3(3x+5)-2x(x^2-4x+4)-[(2x)^2-3^2]`

`=6x^2+10x-9x-15-2x^3+8x^2-8x-4x^2+9`

`=(6x^2-4x^2+8x^2)-2x^3+(10x-9x-8x)+(-15+9)`

Thay `x=-7` vào ta được:

`B=10(-7)^2-2(-7)^3-7(-7)-6`

`=>B=10.49-2(-343)+49-6`

`=>B=490+686+49-6`

`=>B=1219`

=5x^2+5x-2x-2-(5x^2+x-15x-3)-17x-51

=5x^2-14x-53-5x^2+14x+3

=-50

\(=2x^2-2-2x^2+8x+3x-12\)

=11x-14

\(A=\frac{x+3}{x^2-1}-\frac{x+1}{x^2-x}=\frac{x+3}{\left(x-1\right)\left(x+1\right)}-\frac{x+1}{x\left(x-1\right)}\)

     \(=\frac{x\left(x+3\right)-\left(x+1\right)\left(x+1\right)}{x\left(x-1\right)\left(x+1\right)}\)

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

           \(=\frac{1}{x\left(x+1\right)}\)

Chúc bạn học tốt !!!

Ta có: A = \(\frac{x+3}{x^2-1}-\frac{x+1}{x^2-x}\)

=> A = \(\frac{x+3}{\left(x-1\right)\left(x+1\right)}-\frac{x+1}{x\left(x-1\right)}\)

=> A = \(\frac{x\left(x+3\right)}{x\left(x-1\right)\left(x+1\right)}-\frac{\left(x+1\right)^2}{x\left(x-1\right)\left(x+1\right)}\)

=> A = \(\frac{x\left(x+3\right)-\left(x+1\right)^2}{x\left(x-1\right)\left(x+1\right)}\)

=> A  = \(\frac{x^2+3x-x^2-2x-1}{x\left(x-1\right)\left(x+1\right)}\)

=> A = \(\frac{x-1}{x\left(x-1\right)\left(x+1\right)}\)

=> A = \(\frac{1}{x\left(x+1\right)}\) (Đk: x \(\ne\)0 hoặc x \(\ne\)-1)

chịu

(x+2)(x-2)-(x-3)(x+1)

=x²-4-(x²-2x-3)

=x²-4-x²+2x+3

=2x-1

het noi nha trieu dang