Question

Answer 1

a: 

\(A=\dfrac{-\left(x+2\right)^2-4x^2+\left(x-2\right)^2}{\left(x+2\right)\left(x-2\right)}:\dfrac{x\left(x-3\right)}{-x^2\left(x-2\right)}\)

\(=\dfrac{-x^2-4x-4-4x^2+x^2-4x+4}{\left(x+2\right)\left(x-2\right)}\cdot\dfrac{-x\left(x-2\right)}{x-3}\)

\(=\dfrac{-4x^2-8x}{\left(x+2\right)}\cdot\dfrac{-x}{x-3}\)

\(=\dfrac{4x^2}{x-3}\)

b: Để A>0 thì x-3>0

hay x>3

c: =>x-7=4 hoặc x-7=-4

=>x=11(nhận) hoặc x=3(loại)

Thay x=11 vào A, ta được:

\(A=\dfrac{4\cdot11^2}{11-3}=\dfrac{4\cdot121}{8}=\dfrac{121}{2}\)