Question

biết \(\lim\limits_{x\rightarrow+\infty}\left(\dfrac{x^2+1}{x-2}+ax-b\right)=-5\). tìm a, b?

Answer 1

\(\lim\limits_{x\rightarrow+\infty}\left(\dfrac{\left(a+1\right)x^2-\left(2a+b\right)x+2b+1}{x-2}\right)\)

Giới hạn hữu hạn khi \(a+1=0\Rightarrow a=-1\)

Khi đó: \(\lim\limits_{x\rightarrow+\infty}\left(\dfrac{\left(2-b\right)x+2b+1}{x-2}\right)=\lim\limits_{x\rightarrow+\infty}\dfrac{2-b+\dfrac{2b+1}{x}}{1-\dfrac{2}{x}}=2-b=-5\)

\(\Rightarrow b=7\)