題目
Problem
Let f(x)=ex+sin(2x) and g(x)=ex+cos(2x) for x∈(−∞,∞). Which of the following statements is true?
(a) −∞<limx→∞g(x)/f(x)≤1.
(b) 1<limx→∞g(x)/f(x)≤2.
(c) 2<limx→∞g(x)/f(x)≤3.
(d) 3<limx→∞g(x)/f(x)<∞.
(e) limx→∞g(x)/f(x) does not exist.
解答
解法一
思路
展開
- 分子分母同除以 ex;有界三角項除以 ex 均趨近零。
答題過程
展開
f(x)g(x)=1+e−xsin2x1+e−xcos2x⟶1.
答案為 (a)。