Question

等差数列｛an｝等比数列｛bn｝其中a1=b1 a2=b2 a4=b4 两数列公差公比都为d 求｛an｝｛bn｝

Answer 1

a1+d=a2=b2=a1*d,a1*（d-1）=d

a1+3d=a4=b4=a1*d^3,a1*（d^3-1）=3d

二式除一式得：d^2+d+1=3,d=1（舍）或d=-2,a1=2/3

an=2/3-2（n-1）,bn=2/3*（-2）^（n-1）谢谢评价