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10.Prove that cosh (3x) = 4 cosh"x-3 cosh x. |
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Answer» LHS:Cosh (3x) = cosh (2x + x)=cosh 2x cosh x - sin 2x sin x=cosh 2x cosh x - 2 sin ² x cosh x=cosh 2x cosh x - 2 cosh x (1 - cos ² x)=(2 cosh ² x - 1) (cosh x) + 2(cosh ² x - 1))(cosh x)=2 cosh ³ x - cosh x + 2 cosh ³ x - 2 cosh x=4 cosh ³ x - 3 cosh x=RHS LHS = RHS Hence proved |
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