x的平方根：square root of x ;  x的立方根：cube root of x;     x的n次方根：the nth root of x; 

 x!：factorial of x

log_nx：logx to the base n ;    x的n次方：the nth root of x；     x的绝对值：the absolute value of x

x' ：x prime，first derivate of  x ;    x''：x double prime， second derivate of x

x'''：x triple prime，third derivate of x     x' (t)：first derivate of x with respect to time    

x上加一点：x dot,  first derivate of x    

x_1：x sub one；x_n：x sub n