Bài 48. Tìm các giới hạn sau:
a) \(\mathop {\lim }\limits_{x \to 0} {{{e^2} – {e^{3x + 2}}} \over x}\)
b) \(\mathop {\lim }\limits_{x \to 0} {{{e^{2x}} – {e^{5x}}} \over x}\)
Giải
a) \(\mathop {\lim }\limits_{x \to 0} {{{e^2} – {e^{3x + 2}}} \over x} = \mathop {\lim }\limits_{x \to 0} {{{e^2}\left( {1 – {3^{3x}}} \right)} \over x} = – 3{e^2}.\mathop {\lim }\limits_{x \to 0} {{{e^{3x}} – 1} \over {3x}} = – 3{e^2}\).
b) \(\mathop {\lim }\limits_{x \to 0} {{{e^{2x}} – {e^{5x}}} \over x} = \mathop {\lim }\limits_{x \to 0} \left( {{{{e^{2x}} – 1} \over x} – {{{e^{5x}} – 1} \over x}} \right) = 2 – 5 = – 3\).