利用矩形法可以求定积分问题的输入：double a /*积分区间下限*/；double b /*积分区间上限*/

问题的输出：double fx /*积分结果*/-The use of the the rectangle method can find definite integral input: double a　/* integral interval lower limit* /　a double b　/* maximum integration interval*/output: double fx　/* integration result* /