因为x=1*x,所以经常在运算中把1提取出来,原式=1*x+2.5*x,因为都有x,所以可以提取,=(1+2.5)x=3.5x 1*x+2.5*x=0.7 (1+2.5)x=3.5x=0.7 x=0.2
