2a/(2a+3)=2a(3-2a)/(3+2a)(3-2a)=(6a-4a^2)/(9-4a^2)=(4a^2-6a)/(4a^2-9)3/(3-2a)=3(3+2a)/(3+2a)(3-2a)=(9+6a)/(9-4a^2)=(-9-6a)/(4a^2-9)(2a+15)/(4a^2-9)不变.三个分母都是(4a^2-9)若有疑问可以百度Hi聊、...