问题标题: 酷町堂：cmath函数

cmath是c++语言中的库函数,其中的c表示函数是来自c标准库的函数，math为数学常用库函数。cmath库函数列表:

using ::abs; //绝对值　　using ::acos; //反余弦　　using ::acosf; //反余弦　　using ::acosl; //反余弦　　using ::asin; //反正弦　　using ::asinf; //反正弦　　using ::asinl; //反正弦　　using ::atan; //反正切　　using ::atan2; //y/x的反正切　　using ::atan2f; //y/x的反正切　　using ::atan2l; //y/x的反正切　　using ::atanf; //反正切　　using ::atanl; //反正切　　using ::ceil; //上取整　　using ::ceilf; //上取整　　using ::ceill; //上取整　　using ::cos; //余弦　　using ::cosf; //余弦　　using ::cosh; //双曲余弦　　using ::coshf; //双曲余弦　　using ::coshl; //双曲余弦　　using ::cosl; //余弦　　using ::exp; //指数值　　using ::expf; //指数值　　using ::expl; //指数值　　using ::fabs; //绝对值　　using ::fabsf; //绝对值　　using ::fabsl; //绝对值　　using ::floor; //下取整　　using ::floorf; //下取整　　using ::floorl; //下取整　　using ::fmod; //求余　　using ::fmodf; //求余　　using ::fmodl; //求余　　using ::frexp; //返回value=x*2n中x的值,n存贮在eptr中　　using ::frexpf; //返回value=x*2n中x的值,n存贮在eptr中　　using ::frexpl; //返回value=x*2n中x的值,n存贮在eptr中　　using ::ldexp; //返回value*2exp的值　　using ::ldexpf; //返回value*2exp的值　　using ::ldexpl; //返回value*2exp的值　　using ::log; //对数　　using ::log10; //对数　　using ::log10f; //对数　　using ::log10l; //对数　　using ::logf; //对数　　using ::logl; //对数　　using ::modf; //将双精度数value分解成尾数和阶　　using ::modff; //将双精度数value分解成尾数和阶　　using ::modfl; //将双精度数value分解成尾数和阶　　using ::pow; //计算幂　　using ::powf; //计算幂　　using ::powl; //计算幂　　using ::sin; //正弦　　using ::sinf; //正弦　　using ::sinh; //双曲正弦　　using ::sinhf; //双曲正弦　　using ::sinhl; //双曲正弦　　using ::sinl; //正弦　　using ::sqrt; //开方　　using ::sqrtf; //开方　　using ::sqrtl; //开方　　using ::tan; //正切　　using ::tanf; //正切　　using ::tanh; //双曲正切　　using ::tanhf; //双曲正切　　using ::tanhl; //双曲正切　　using ::tanl; //正切