看符号 arctan(正无穷大)=二分之派arctan(负无穷大)=负二分之派x->1+ arctan(1/(1-x))=arctan(负无穷大)=负二分之派x->1- arctan(1/(1-x))=arctan(正无穷大)=二分之派x->-1 arctan(1/(1-x))=arctan(1/2)
