写出下列数列的前5项.1.a1=1,a2=2,an+2=2an+1+an2.a1=-1,a2=-2,an+2=1/(an+1)+1/an

Question

写出下列数列的前5项.
1.a1=1,a2=2,an+2=2an+1+an
2.a1=-1,a2=-2,an+2=1/(an+1)+1/an

Answer 1

1.a1=1,a2=2,an+2=2an+1+an
a1=1,a2=2,a3=2a2+a1=5,a4=2a3+a2=12,a5=2a4+a3=29
2.a1=-1,a2=-2,an+2=1/(an+1)+1/an
a1=-1,a2=-2,
a3=1/(a2)+1/a1=1/（-2）+1/（-1）=-3/2
a4=1/(a3)+1/a2=1/（-3/2）+1/（-2）=-7/6
a5=1/(a4)+1/a3=1/（-7/6）+1/（-3/2）=-32/21