21.1 若2,X,Y,Z,18 ,成等比数列,则X=
2个回答
a1=2
a5=18
a5=a1*q^4=2*q^4=18
q^4=9
q=根号3或-根号3
x=a1*q=2根号3或-2根号3
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解下列方程与:2x+y+z=17x+2y+z=18x+y+2z=21