数学考试会遇到一些题看起来比较难算,但如果知道(回忆起)定理/规律以后就很简单的题。这里列出五个知识点,考前大家可以再看看。平时做数学题遇到比较有意思的题或者定理/规律也可以在文章最后留言哦。
1. 圆的内接三角形,当一边为圆直径时,必为直角三角形。
2. 约数个数定理
首先,n可以分解质因数:n=p1^a1×p2^a2×p3^a3*…*pk^ak,
由约数定义可知p1^a1的约数有:p1^0, p1^1, p1^2……p1^a1 ,共(a1+1)个;同理p2^a2的约数有(a2+1)个……pk^ak的约数有(ak+1)个。
故根据乘法原理:n的约数的个数就是(a1+1)(a2+1)(a3+1)…(ak+1)。
3. 标准差
序列中每一个数都加上一个常数,标准方差保持不变。
Quantity A: The standard deviation of a set of 5 different integers, each of which is between 0 and 10
Quantity B: The standard deviation of a set of 5 different integers, each of which is between 10 and 20
A. Quantity A is greater.
B. Quantity B is greater.
C. The two quantities are equal.
D. The relationship cannot be determined from the information given.
If d is the standard deviation of x, y, and z, what is the standard deviation of x + 5, y + 5, and z + 5 ?
A. d
B. 3d
C. 15d
D. d + 5
E. d + 15
4. 任何三个连续的正整数的乘积必然可以被3和6整除
5. 幂的个位数特性
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