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If ` sin alpha =(1)/(2) ,` prove that `(3 cos alpha - 4 cos ^(3) alpha )=0.`

Answer» `cos ^(2) alpha =(1- sin ^(2) alpha )=(1-(1)/(4))=(3)/(4)implies cos alpha =(sqrt(3))/(2).`
`therefore (3 cos alpha -4cos ^(3)alpha)=(3xx(sqrt(3))/(2)-4xx(3sqrt(3))/(8))=((3sqrt(3))/(2) -(3sqrt(3))/(2))=0.`


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