Question

if 2costheta =x+1/x, prove that 2cos3theta =x3+1/x3​

Answer 1

Step-by-step explanation:

x+1/x=2cosA

(x+1/x)³=(2cosA)³

x³+1/x³+3×x×1/x(x+1/x)=8cos³A

x³+1/x³=8cos³A-3(2cosA)

=8cos³A-6cosA

=2(4cos³A-3cosA)

=2cos3A

{cos3A=4cos³A-3cosA}formula

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