Let xn represent a number in the form of x with n fraction lines. Then, we have xn+1=1+xn1.
It is easy to find x1=21,x2=32,x3=53,x4=85,
⋯. Let yn=xn2+xn, then
y1=431,y3=25241$.Conjecture:when$n$isodd,$yn1$.Wewillprovethisconjecture.
∵yn+1−1=xn+12+xn+1−1=(1+xn1)2+(1+xn1)−1=(1+xn1)2[1+(1+xn)−(1+xn)2]=−(1+xn1)2(xn2+xn−1)=−(1+xn1)2(yn−1),
$∴yn+1−1$hastheoppositesignof$yn−1$,whichmeanstheconjectureistrue.Thus,$y1000>1$.
x 2 +x>1 {. }