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Grade: 12th pass

                        

Prove that , (sinX) 3 × sin3X + (cosX) 3 × cos3X =(cos2X) 3

2 years ago

Answers : (1)

Susmita
425 Points
							
Use the formula
sin3x=(3sinx-sin3x)/4
and cos3x=(3cosx+cos3x)/4
also cos3(2x)=(3cos2x+cos6x)/4
Put the first two formula in the given expression.you will get
(3sinxsin3x-sin23x+3cosxcos3x+cos23x)/4
Put 3sinxsin3x+3cosxcos3x=cos(3x-x)=cos2x
And cos23x-sin23x=cos(2.3x)=cos6x.
and see you will get the ans.
 
2 years ago
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