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Question Number 41704 by abdo.msup.com last updated on 11/Aug/18
$${let}\:{u}_{{n}} =\:\frac{\mathrm{1}}{\sqrt{{n}−\mathrm{1}}}\:+\frac{\mathrm{2}}{\sqrt{{n}}}\:+\frac{\mathrm{1}}{\sqrt{{n}+\mathrm{1}}} \\ $$$${calculate}\:\sum_{{n}=\mathrm{2}} ^{\infty} \:{u}_{{n}} \\ $$