计算下列定积分: ∫201/(1+3x)2dx

计算下列定积分:
201/(1+3x)2dx
【正确答案】:∫201/(1+3x)2dx =1/3∫201/(1+3x)2d(1+3x) =1/3(-1/(1+3x)|20 =-1/3×(1/7-1) =2/7