在数列{an}中,a1=1,a2=5,an+2=an+1-an (n∈N*),则a100等于( an+2=an+1-an,an+3=an+2-an+1,两式相加可得
在数列{an}中,a1=1,a2=5,an+2=an+1-an (n∈N*),则a100等于( )方法一:an+2=an+1-an,an+3=an+2-an+1,两式相加可得an+3=-an,an+6=an,∴a100=a16×6+4=a4=-1.an+6=an,∴a100=a16×6+4=a4=-1.为什么这样做?