Tính giới hạn sau : \(Lim_{x\rightarrow2}\frac{2x^3+5x^2-7x+2}{x^2-3x+2}\)
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\(\dfrac{lim}{x\rightarrow2}\dfrac{x^2-3x+3}{x-2}\)
ta có : \(\dfrac{lim}{x\rightarrow2}\dfrac{x^2-3x+3}{ }=1\) và \(\dfrac{lim}{x\rightarrow2}\dfrac{x-2}{ }=0\)
\(\Rightarrow\dfrac{lim}{x\rightarrow2}\dfrac{x^2-3x+3}{x-2}=\infty\)
và \(\dfrac{lim}{x\rightarrow2}\dfrac{x^2-3x+3}{x-2}=+\infty\) khi \(x>2\)
\(\dfrac{lim}{x\rightarrow2}\dfrac{x^2-3x+3}{x-2}=-\infty\) khi \(x< 2\)
\(\lim\limits_{x\rightarrow2}\dfrac{2x^3+5x^2-7x+2}{x^2-3x+2}\)
\(=\lim\limits_{x\rightarrow2}\dfrac{2x^3-4x^2+9x^2-18x+11x-22+24}{\left(x-2\right)\left(x+1\right)}\)
\(=\lim\limits_{x\rightarrow2}\dfrac{\left(x-2\right)\left(2x^2+9x+11\right)+24}{\left(x-2\right)\left(x+1\right)}\)
\(=+\infty\) vì \(\left\{{}\begin{matrix}\lim\limits_{x\rightarrow2}\left(x-2\right)\left(2x^2+9x+11\right)+24=24>0\\\lim\limits_{x\rightarrow2}\left(x-2\right)=2-2=0\\\lim\limits_{x\rightarrow2}x+1=2+1=3>0\end{matrix}\right.\)
a/ \(\lim\limits_{x\rightarrow2}\dfrac{2+3}{4+2+4}=\dfrac{5}{10}=\dfrac{1}{2}\)
b/ \(\lim\limits_{x\rightarrow-3}\dfrac{\left(x+2\right)\left(x+3\right)}{x\left(x+3\right)}=\lim\limits_{x\rightarrow-3}\dfrac{x+2}{x}=\dfrac{-3+2}{-3}=\dfrac{1}{3}\)
Bạn tự hiểu là giới hạn khi x tới 2:
\(=\frac{x\left(x-2\right)\left[2\sqrt{x+2}+3x-2\right]}{4\left(x+2\right)-\left(3x-2\right)^2}=\frac{x\left(x-2\right)\left[2\sqrt{x+2}+3x-2\right]}{-9x^2+16x+4}=\frac{x\left(x-2\right)\left[2\sqrt{x+2}+3x-2\right]}{\left(x-2\right)\left(-9x-2\right)}\)
\(=\frac{x\left[2\sqrt{x+2}+3x-2\right]}{-9x-x}=\frac{2\left[2\sqrt{4}+6-2\right]}{-18-2}=...\)
a: \(=lim_{x->-\infty}\dfrac{2x-5+\dfrac{1}{x^2}}{7-\dfrac{1}{x}+\dfrac{4}{x^2}}\)
\(=\dfrac{2x-5}{7}\)
\(=\dfrac{2}{7}x-\dfrac{5}{7}\)
\(=-\infty\)
b: \(=lim_{x->+\infty}x\sqrt{\dfrac{1+\dfrac{1}{x}+\dfrac{3}{x^2}}{3x^2+4-\dfrac{5}{x^2}}}\)
\(=lim_{x->+\infty}x\sqrt{\dfrac{1}{3x^2+4}}=+\infty\)
\(L=\lim\limits_{x\rightarrow2}\frac{x-\sqrt{3x-2}}{x^2-4}\)
\(=\lim\limits_{x\rightarrow2}\frac{x^2-3x+2}{\left(x-4\right)\left(x+\sqrt{3x-2}\right)}=\lim\limits_{x\rightarrow2}\frac{\left(x-2\right)\left(x-1\right)}{\left(x-2\right)\left(x+2\right)\left(x+\sqrt{3x-2}\right)}\)
\(=\lim\limits_{x\rightarrow2}\frac{x-1}{\left(x+2\right)\left(x+\sqrt{3x-2}\right)}=\frac{1}{16}\)
\(lim_{x\rightarrow2^+}\frac{2x^3+5x^2-7x+2}{x^2-3x+2}=\frac{24}{0^+}=+\infty\)
\(lim_{x\rightarrow2^-}\frac{2x^3+5x^2-7x+2}{x^2-3x+2}=\frac{24}{0^-}=-\infty\)
do đó \(lim_{x\rightarrow2}\frac{2x^3+5x^2-7x+2}{x^2-3x+2}\)không tồn tại.
\(Lim_{x\rightarrow2}\frac{2x^3+5x^2-7x+2}{x^2-3x+2}=Lim_{x\rightarrow2}\frac{\left(2x-1\right)\left(x^2+3x-2\right)}{x^2-3x+2}\)
\(=Lim_{x\rightarrow2}=\frac{\left(2x-1\right)\left(x^2+3x-2\right)}{\left(x-1\right)\left(x-2\right)}=\infty\)
Vì giới hạn của tử bằng 24 , giới hạn của mẫu bằng 0
Vậy \(Lim_{x\rightarrow2}\frac{2x^3+5x^2-7x+2}{x^2-3x+2}=\infty\)
P/s : Lâu lắm không học giờ làm sai thì thôi vậy