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tanhx=(ex−e−x)(ex+e−x) Let a=ex b=1ex ∴tanhx=a−ba+b 23=a−ba+b 2a+2b=3a−3b a=5b ab=e2x 2x=log(a/b) ∴x=0.5log(5) ∴cosh2x=cosh(log5) ∴cosh2x=2.6