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Find a positive fixed point and prove decrease above it

Positive real terms satisfy xn+1=2xn+1x_{n+1}=2\sqrt{x_n+1}.

(i) If the sequence converges, show its limit is 2+222+2\sqrt2.

(ii) Prove xn+1<xnx_{n+1}<x_n whenever xn>2+22x_n>2+2\sqrt2.

[2010/TJC/JC2/MYE/1]

CJC · Discussion · Question 14

Check the sign of the fixed point after squaring, then compare positive quantities.

Read the worked solution