1.

Prove that `cos 60^(@)=cos^(2)30^(@)-sin^(2)30^(@)`.

Answer» `LHS=cos 60^(@)`
`=(1)/(2)`
`RHS=cos^(2)30^(@)-sin^(2)30^(@)`
`=((sqrt(3))/(2))^(2)-((1)/(2))^(2)=(3)/(4)-(1)/(4)=(3-1)/(4)`
`=(2)/(4)=(1)/(2)`.
`therefore LHS=RHS`. (Proved)


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