a分之3+4a分之1 =12/4a+1/4a=13/(4a) a+b分之a平方+a-b分之b平方-2ab=a²/(a+b)+(b²-2ab)/(a-b)=(a³-a²b+ab²+b³-2a²b-2ab²)(a+b)(a-b)=(a³-3a²b-ab²+b³...