问题
选择题
已知数列{an}中,a1=1,a2=2,an+2=an+1+an,则a5等于( )
A.13
B.8
C.5
D.9
答案
∵a1=1,a2=2,an+2=an+1+an,∴a3=1+2=3,∴a4=3+2=5,a5=5+3=8,
故选B.
已知数列{an}中,a1=1,a2=2,an+2=an+1+an,则a5等于( )
A.13
B.8
C.5
D.9
∵a1=1,a2=2,an+2=an+1+an,∴a3=1+2=3,∴a4=3+2=5,a5=5+3=8,
故选B.