(1/2a的平方+1/3a)+2(1/3a-1/4a的二次方)-(1/4a+1/5)=1/2a的平方+1/3a+2/3a-1/2a的平方-1/4a-1/5=3/4a-1/5=3/4*10-1/5=7.3
