互为相反数则相加等于0 (x-1)/2+(3x+4)/2=0 两边乘2 x-1+3x+4=0 4x+3=0 x=-3/4
x-1/2 与3x+4/2 的值互为相反数（x-1）/2 + (3x+4)/2 = 0解得 x= - 3/4
x= - 3/4
