一、选择题部分详解
1. 题目回顾
(1)若函数\(f(x) = x^3 - 3x + 1\)的图像关于点\((1,0)\)对称,则\(f(0) = \, ?\)
(2)在\(\triangle ABC\)中,\(a = 3\),\(b = 4\),\(c = 5\),则\(\cos A + \cos B + \cos C = \, ?\)
2. 解答思路
(1)解答思路
由于函数\(f(x)\)的图像关于点\((1,0)\)对称,则\(f(1 + x) = -f(1 - x)\)。将\(x = 0\)代入,得\(f(1) = -f(1)\),即\(f(1) = 0\)。又因为\(f(1) = 1^3 - 3 \times 1 + 1 = -1\),所以\(f(0) = -f(1) = 1\)。
(2)解答思路
由余弦定理,得\(\cos A = \frac{b^2 + c^2 - a^2}{2bc} = \frac{4^2 + 5^2 - 3^2}{2 \times 4 \times 5} = \frac{2}{5}\)。同理,\(\cos B = \frac{a^2 + c^2 - b^2}{2ac} = \frac{3^2 + 5^2 - 4^2}{2 \times 3 \times 5} = \frac{1}{2}\),\(\cos C = \frac{a^2 + b^2 - c^2}{2ab} = \frac{3^2 + 4^2 - 5^2}{2 \times 3 \times 4} = \frac{1}{4}\)。所以\(\cos A + \cos B + \cos C = \frac{2}{5} + \frac{1}{2} + \frac{1}{4} = \frac{13}{20}\)。
二、填空题部分详解
1. 题目回顾
(1)设数列\(\{a_n\}\)的通项公式为\(a_n = 2^n - 1\),则\(a_{2017} = \, ?\)
(2)已知函数\(f(x) = \frac{x^2 - 1}{x - 1}\),则\(f'(1) = \, ?\)
2. 解答思路
(1)解答思路
由数列的通项公式,得\(a_{2017} = 2^{2017} - 1\)。
(2)解答思路
对函数\(f(x)\)求导,得\(f'(x) = \frac{2x}{(x - 1)^2}\)。将\(x = 1\)代入,得\(f'(1) = \frac{2 \times 1}{(1 - 1)^2}\),由于分母为0,所以\(f'(1)\)不存在。
三、解答题部分详解
1. 题目回顾
(1)已知函数\(f(x) = x^3 - 3x + 1\),求\(f(x)\)的极值。
(2)已知数列\(\{a_n\}\)的通项公式为\(a_n = 2^n - 1\),求\(\lim_{n \to \infty} \frac{a_n}{3^n}\)。
2. 解答思路
(1)解答思路
对函数\(f(x)\)求导,得\(f'(x) = 3x^2 - 3\)。令\(f'(x) = 0\),解得\(x = \pm 1\)。当\(x < -1\)时,\(f'(x) > 0\);当\(-1 < x < 1\)时,\(f'(x) < 0\);当\(x > 1\)时,\(f'(x) > 0\)。所以\(f(x)\)在\(x = -1\)处取得极大值\(f(-1) = 3\),在\(x = 1\)处取得极小值\(f(1) = -1\)。
(2)解答思路
由数列的通项公式,得\(\lim_{n \to \infty} \frac{a_n}{3^n} = \lim_{n \to \infty} \frac{2^n - 1}{3^n} = \lim_{n \to \infty} \left(\frac{2}{3}\right)^n - \lim_{n \to \infty} \frac{1}{3^n} = 0 - 0 = 0\)。
四、答案揭晓
- 选择题: (1)\(f(0) = 1\) (2)\(\cos A + \cos B + \cos C = \frac{13}{20}\)
- 填空题: (1)\(a_{2017} = 2^{2017} - 1\) (2)\(f'(1)\)不存在
- 解答题: (1)\(f(x)\)的极大值为3,极小值为-1 (2)\(\lim_{n \to \infty} \frac{a_n}{3^n} = 0\)
