因为Y=(1/2)是减函数,所以(X-1)(X-3)=X的平方-4X+3=(X-2)的平方-1
在(-无穷,2)上单调递增,在(2,+无穷)上单调递减
而定义域是(-无穷,1)并(3,+无穷),所以单调增区间是(根号3,+无穷)
减区间是(-无穷,1)