a) Ta có \(t = \frac{1}{x},\) nên khi x tiến đến 0 thì t tiến đến dương vô cùng do đó

\(\mathop {\lim }\limits_{x \to 0} {\left( {1 + x} \right)^{\frac{1}{x}}} = \mathop {\lim }\limits_{t \to  + \infty } {\left( {1 + \frac{1}{t}} \right)^t} = e\)

b) \(\ln y = \ln {\left( {1 + x} \right)^{\frac{1}{x}}} = \frac{1}{x}\ln \left( {1 + x} \right)\)

\(\mathop {\lim }\limits_{x \to 0} \ln y = \mathop {\lim }\limits_{x \to 0} \frac{{\ln \left( {1 + x} \right)}}{x} = 1\)

c) \(t = {e^x} - 1 \Leftrightarrow {e^x} = t + 1 \Leftrightarrow x = \ln \left( {t + 1} \right)\)

\(\mathop {\lim }\limits_{x \to 0} \frac{{{e^x} - 1}}{x} = \mathop {\lim }\limits_{t \to 0} \frac{t}{{\ln \left( {t + 1} \right)}} = 1\)

a) \(lim\dfrac{-2n+1}{n}=lim\dfrac{\dfrac{-2n}{n}+\dfrac{1}{n}}{\dfrac{n}{n}}=lim\dfrac{-2+\dfrac{1}{n}}{1}=\dfrac{lim\left(-2\right)+\dfrac{lim1}{n}}{lim1}=\dfrac{-2+0}{1}=-\dfrac{2}{1}=-2\)

b) \(\lim\limits_{x\rightarrow1}\dfrac{3-\sqrt{x+8}}{x-1}=\lim\limits_{x\rightarrow1}\dfrac{9-\left(x+8\right)}{\left(x-1\right)\left(3+\sqrt{x+8}\right)}=\lim\limits_{x\rightarrow1}\dfrac{x-1}{\left(x-1\right)\left(3+\sqrt{x+8}\right)}=\lim\limits_{x\rightarrow1}\dfrac{1}{3+\sqrt{x+8}}=\dfrac{1}{3+\sqrt{1+8}}=\dfrac{1}{3+3}=\dfrac{1}{9}\)

a) \(\mathop {\lim }\limits_{x \to  + \infty } \frac{{ - x + 2}}{{x + 1}} = \mathop {\lim }\limits_{x \to  + \infty } \frac{{x\left( { - 1 + \frac{2}{x}} \right)}}{{x\left( {1 + \frac{1}{x}} \right)}} = \mathop {\lim }\limits_{x \to  + \infty } \frac{{ - 1 + \frac{2}{x}}}{{1 + \frac{1}{x}}} = \frac{{\mathop {\lim }\limits_{x \to  + \infty } \left( { - 1} \right) + \mathop {\lim }\limits_{x \to  + \infty } \frac{2}{x}}}{{\mathop {\lim }\limits_{x \to  + \infty } 1 + \mathop {\lim }\limits_{x \to  + \infty } \frac{1}{x}}} = \frac{{ - 1 + 0}}{{1 + 0}} =  - 1\)

b) \(\mathop {\lim }\limits_{x \to  - \infty } \frac{{x - 2}}{{{x^2}}} = \mathop {\lim }\limits_{x \to  - \infty } \frac{{x\left( {1 - \frac{2}{x}} \right)}}{{{x^2}}} = \mathop {\lim }\limits_{x \to  - \infty } \frac{1}{x}.\mathop {\lim }\limits_{x \to  - \infty } \left( {1 - \frac{2}{x}} \right)\)

                                \( = \mathop {\lim }\limits_{x \to  - \infty } \frac{1}{x}.\left( {\mathop {\lim }\limits_{x \to  - \infty } 1 - \mathop {\lim }\limits_{x \to  - \infty } \frac{2}{x}} \right) = 0.\left( {1 - 0} \right) = 0\).

a) \(\mathop {\lim }\limits_{x \to {3^ - }} \frac{{2x}}{{x - 3}} = \mathop {\lim }\limits_{x \to {3^ - }} \left( {2x} \right).\mathop {\lim }\limits_{x \to {3^ - }} \frac{1}{{x - 3}}\)

Ta có: \(\mathop {\lim }\limits_{x \to {3^ - }} \left( {2x} \right) = 2\mathop {\lim }\limits_{x \to {3^ - }} x = 2.3 = 6;\mathop {\lim }\limits_{x \to {3^ - }} \frac{1}{{x - 3}} =  - \infty \)

\( \Rightarrow \mathop {\lim }\limits_{x \to {3^ - }} \frac{{2x}}{{x - 3}} =  - \infty \)

b) \(\mathop {\lim }\limits_{x \to  + \infty } \left( {3x - 1} \right) = \mathop {\lim }\limits_{x \to  + \infty } x\left( {3 - \frac{1}{x}} \right) = \mathop {\lim }\limits_{x \to  + \infty } x.\mathop {\lim }\limits_{x \to  + \infty } \left( {3 - \frac{1}{x}} \right)\)

Ta có: \(\mathop {\lim }\limits_{x \to  + \infty } x =  + \infty ;\mathop {\lim }\limits_{x \to  + \infty } \left( {3 - \frac{1}{x}} \right) = \mathop {\lim }\limits_{x \to  + \infty } 3 - \mathop {\lim }\limits_{x \to  + \infty } \frac{1}{x} = 3 - 0 = 3\)

\( \Rightarrow \mathop {\lim }\limits_{x \to  + \infty } \left( {3x - 1} \right) =  + \infty \)

a) \(\mathop {\lim }\limits_{x \to  - 2} \left( {{x^2} + 5x - 2} \right) = \mathop {\lim }\limits_{x \to  - 2} {x^2} + \mathop {\lim }\limits_{x \to  - 2} \left( {5x} \right) - \mathop {\lim }\limits_{x \to  - 2} 2\)

\( = \mathop {\lim }\limits_{x \to  - 2} {x^2} + 5\mathop {\lim }\limits_{x \to  - 2} x - \mathop {\lim }\limits_{x \to  - 2} 2 = {\left( { - 2} \right)^2} + 5.\left( { - 2} \right) - 2 =  - 8\)

b) \(\mathop {\lim }\limits_{x \to 1} \frac{{{x^2} - 1}}{{x - 1}} = \mathop {\lim }\limits_{x \to 1} \frac{{\left( {x - 1} \right)\left( {x + 1} \right)}}{{x - 1}} = \mathop {\lim }\limits_{x \to 1} \left( {x + 1} \right) = \mathop {\lim }\limits_{x \to 1} x + \mathop {\lim }\limits_{x \to 1} 1 = 1 + 1 = 2\)

a) \(\mathop {\lim }\limits_{x \to  + \infty } \frac{{1 - 3{x^2}}}{{{x^2} + 2x}} = \mathop {\lim }\limits_{x \to  + \infty } \frac{{{x^2}\left( {\frac{1}{{{x^2}}} - 3} \right)}}{{{x^2}\left( {1 + \frac{{2x}}{{{x^2}}}} \right)}} = \mathop {\lim }\limits_{x \to  + \infty } \frac{{\frac{1}{{{x^2}}} - 3}}{{1 + \frac{2}{x}}} = \frac{{\mathop {\lim }\limits_{x \to  + \infty } \frac{1}{{{x^2}}} - \mathop {\lim }\limits_{x \to  + \infty } 3}}{{\mathop {\lim }\limits_{x \to  + \infty } 1 + \mathop {\lim }\limits_{x \to  + \infty } \frac{2}{x}}} = \frac{{0 - 3}}{{1 + 0}} =  - 3\)

b) \(\mathop {\lim }\limits_{x \to  - \infty } \frac{2}{{x + 1}} = \mathop {\lim }\limits_{x \to  - \infty } \frac{2}{{x\left( {1 + \frac{1}{x}} \right)}} = \mathop {\lim }\limits_{x \to  - \infty } \frac{1}{x}.\mathop {\lim }\limits_{x \to  - \infty } \frac{2}{{1 + \frac{1}{x}}} = \mathop {\lim }\limits_{x \to  - \infty } \frac{1}{x}.\frac{{\mathop {\lim }\limits_{x \to  - \infty } 2}}{{\mathop {\lim }\limits_{x \to  - \infty } 1 + \mathop {\lim }\limits_{x \to  - \infty } \frac{1}{x}}} = 0.\frac{2}{{1 + 0}} = 0\).

a) \(\mathop {\lim }\limits_{x \to  - 3} {x^2};\)            

Giả sử \(\left( {{x_n}} \right)\) là dãy số bất kì thỏa mãn \(\lim {x_n} =  - 3.\)

Ta có \(\lim x_n^2 = {\left( { - 3} \right)^2} = 9\)

Vậy \(\mathop {\lim }\limits_{x \to  - 3} {x^2} = 9.\)

b) \(\mathop {\lim }\limits_{x \to 5} \frac{{{x^2} - 25}}{{x - 5}}.\)

Giả sử \(\left( {{x_n}} \right)\) là dãy số bất kì thỏa mãn \(\lim {x_n} = 5.\)

Ta có \(\lim \frac{{{x_n}^2 - 25}}{{{x_n} - 5}} = \lim \frac{{\left( {{x_n} - 5} \right)\left( {{x_n} + 5} \right)}}{{{x_n} - 5}} = \lim \left( {{x_n} + 5} \right) = \lim {x_n} + 5 = 5 + 5 = 10\)

Vậy \(\mathop {\lim }\limits_{x \to 5} \frac{{{x^2} - 25}}{{x - 5}} = 10.\)

a: \(\lim\limits_{x\rightarrow-1^+}x+1=0\)

=>\(\lim\limits_{x\rightarrow-1^+}\dfrac{1}{x+1}=+\infty\)

b: \(\lim\limits_{x\rightarrow-\infty}1-x^2=\lim\limits_{x\rightarrow-\infty}\left[x^2\left(\dfrac{1}{x^2}-1\right)\right]\)

\(=-\infty\)

c: \(\lim\limits_{x\rightarrow3^-}\dfrac{x}{3-x}=\lim\limits_{x\rightarrow3^-}=\dfrac{-x}{x-3}\)

\(\lim\limits_{x\rightarrow3^-}x-3=0\)

\(\lim\limits_{x\rightarrow3^-}-x=3>0\)

=>\(\lim\limits_{x\rightarrow3^-}\dfrac{x}{3-x}=+\infty\)

a) \(\mathop {\lim }\limits_{x \to  - 1} \left( {3{x^2} - x + 2} \right) = \mathop {\lim }\limits_{x \to  - 1} \left( {3{x^2}} \right) - \mathop {\lim }\limits_{x \to  - 1} x + \mathop {\lim }\limits_{x \to  - 1} 2\)

                                                \( = 3\mathop {\lim }\limits_{x \to  - 1} \left( {{x^2}} \right) - \mathop {\lim }\limits_{x \to  - 1} x + \mathop {\lim }\limits_{x \to  - 1} 2 = 3.{\left( { - 1} \right)^2} - \left( { - 1} \right) + 2 = 6\)

b) \(\mathop {\lim }\limits_{x \to 4} \frac{{{x^2} - 16}}{{x - 4}} = \mathop {\lim }\limits_{x \to 4} \frac{{\left( {x - 4} \right)\left( {x + 4} \right)}}{{x - 4}} = \mathop {\lim }\limits_{x \to 4} \left( {x + 4} \right) = \mathop {\lim }\limits_{x \to 4} x + \mathop {\lim }\limits_{x \to 4} 4 = 4 + 4 = 8\)

c) \(\mathop {\lim }\limits_{x \to 2} \frac{{3 - \sqrt {x + 7} }}{{x - 2}} = \mathop {\lim }\limits_{x \to 2} \frac{{\left( {3 - \sqrt {x + 7} } \right)\left( {3 + \sqrt {x + 7} } \right)}}{{\left( {x - 2} \right)\left( {3 + \sqrt {x + 7} } \right)}} = \mathop {\lim }\limits_{x \to 2} \frac{{{3^2} - \left( {x + 7} \right)}}{{\left( {x - 2} \right)\left( {3 + \sqrt {x + 7} } \right)}}\)

                                         \( = \mathop {\lim }\limits_{x \to 2} \frac{{2 - x}}{{\left( {x - 2} \right)\left( {3 + \sqrt {x + 7} } \right)}} = \mathop {\lim }\limits_{x \to 2} \frac{{ - \left( {x - 2} \right)}}{{\left( {x - 2} \right)\left( {3 + \sqrt {x + 7} } \right)}} = \mathop {\lim }\limits_{x \to 2} \frac{{ - 1}}{{3 + \sqrt {x + 7} }}\)

                                         \( = \frac{{\mathop {\lim }\limits_{x \to 2} \left( { - 1} \right)}}{{\mathop {\lim }\limits_{x \to 2} 3 + \sqrt {\mathop {\lim }\limits_{x \to 2} x + \mathop {\lim }\limits_{x \to 2} 7} }} = \frac{{ - 1}}{{3 + \sqrt {2 + 7} }} =  - \frac{1}{6}\)

a: \(\lim\limits_{x\rightarrow-2}x^2-7x+4=\left(-2\right)^2-7\cdot\left(-2\right)+4=22\)

b: \(\lim\limits_{x\rightarrow3}\dfrac{x-3}{x^2-9}=\lim\limits_{x\rightarrow3}\dfrac{1}{x+3}=\dfrac{1}{3+3}=\dfrac{1}{6}\)

c: \(\lim\limits_{x\rightarrow1}\dfrac{3-\sqrt{x+8}}{x-1}=\lim\limits_{x\rightarrow1}\dfrac{9-x-8}{3+\sqrt{x+8}}\cdot\dfrac{1}{x-1}=\lim\limits_{x\rightarrow1}\dfrac{-1}{3+\sqrt{x+8}}\)

\(=-\dfrac{1}{6}\)