转载来自kb神的推荐：http://cplusplus.com/reference/clibrary/cmath/
很多基础的东西都没有记住啊
注意数据类型的定义，貌似用double比较保险的说。。。
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cmath (math.h)
C numerics library
cmath declares a set of functions to compute common mathematical operations and transformations:Trigonometric functions:
- cos
- Compute cosine (function) 计算余弦
- sin
- Compute sine (function) 计算正弦
- tan
- Compute tangent (function) 计算正切
- acos
- Compute arc cosine (function) 计算反余弦
- asin
- Compute arc sine (function) 计算反正弦
- atan
- Compute arc tangent (function) 计算反正切
- atan2
- Compute arc tangent with two parameters (function) 计算反正切与两个参数
Hyperbolic functions:
- cosh
- Compute hyperbolic cosine (function) 计算双曲余弦
- sinh
- Compute hyperbolic sine (function) 计算双曲正弦
- tanh
- Compute hyperbolic tangent (function) 计算双曲正切
Exponential and logarithmic functions:
- exp
- Compute exponential function (function) 计算指数函数
- frexp
- Get significand and exponent (function) 得到有效数字和指数
- ldexp
- Generate number from significand and exponent (function)生成数字和指数有效数字
- log
- Compute natural logarithm (function) 计算自然对数
- log10
- Compute common logarithm (function) 计算常用对数
- modf
- Break into fractional and integral parts (function) 闯入分数和不可分割的组成部分
Power functions
- pow
- Raise to power (function )
- sqrt
- Compute square root (function)计算平方根
Rounding, absolute value and remainder functions:
- ceil
- Round up value (function) 返回大于或者等于指定表达式的最小整数
- fabs
- Compute absolute value (function) 计算绝对值
- floor
- Round down value (function) 四舍五入价值
- fmod
- Compute remainder of division (function) 求模运算