2,7,28,63,( ),215 A．125 B.126 C.127 D.128

2,7,28,63,( ),215 A．125 B.126 C.127 D.128 因式分解a^3-7a^2-4a+28 已知a满足等式a^2-a-1=0,求代数式a^8+7a^-4的值解：由a^2-a-1=0得,a^2=a+1, 于是a^4=(a+1)^2=a^2+2a+1=3a+2 a^8=(3a+2)^2=9a^2+12a+4=21a+13 a^8+7a^-4=21a+13+7/(3a+2) =(63a^2+81a+26+7)/(3a+2) =(63a+63+81a+33)/(3a+2) =(144a+96)/(3a+2)=48 请 （28a^3-28a^2+7a）÷7a 若a=2,则(-28a²+7a)÷7a的值是? 若a=2,则(-28a²+7a)÷7a的值是? 计算题:(28a^3-21a^2+7a)÷(7a) （a+2)(a-2)(a二次方-a)+(2+a)(3-a)(a+3) （a+2)(a-2)(a二次方-7)+(2+a)(3-a)(a+3) 在等比数列{a(n)}中,a(2)+a(3)=7,a(4)+a(5)=28,则a(5)+a(6)=? a-2a+3a-4a+5a-6a+7a-8a+9a-10a+11a.+99a-100a= 5(a*a*b-3*a*a*b)-2*(a*a*b-7*a*b*b) 2a-5a-7a=? 2a-5a-7a= [-a*(-2a)^3*(-a)^5]^7 2,7,28,63,126,( )A.215 B.216 C.217 D.218 2,7,28,63,126（）A.215 B.216 C.217 D.218 2,7,28,63,( ),215A.125 B.126 C.127 D.128选哪个? 7a+3a^2+2a-a^2+3