(9-a²)/(a²-8a+16)÷(9+6a+a²)/(16-a²)=-(a+3)(a-3)/(a-4)²×[-(a+4)(a-4)/(a+3)²]=(a+3)(a-3)/(a-4)²×(a+4)(a-4)/(a+3)²=(a-3)(a+4)/(a-4)(a+3)=(a²+a-12)/(a²...9减a的平方分之a的平方加8a加16除以9加6a加a的平方分之16减a的平方采纳我，重新问