在线等,谢谢!
边数=(内角和+外角和)÷180°=(1260°+360°)÷180°=162/18=9//A错误(1/a-1)/(a-1)=[(1-a)/a]/(a-1)=-1/aB错误(-a-b)/c=-(a+b)/cC错误2x/(3x+5)-2=2x/(3x+5)-(6x+10)/(3x+5)=(-4x-10)/(3x+5)分式用通分,而不是去分母。D错误a/(a-1)²+1/(1-a)²=a/(a-1)²+1/(a-1)²=(a+1)/(a-1)²分子是单项式,应该用括号。