y=(x-1)(x-3)/(x-1)(2x+1)==>x不等于1y=(x-3)/(2x+1)==>y不等于-2/3y=1/2-7/(4x+2)==>y的值域 (负无穷,-2/3)U(-2/3,1/2)U(1/2,正无穷)
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