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sin4A=4sinAcos^3A-4cosAsin^3A...

`sin4A=4sinAcos^3A-4cosAsin^3A`

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`L.H.S=sin4A`
`RHS=4sinAcos^3A−4sin^3AcosA`
Let the consider `L.H.S =sin4A => 2sin2Acos2A`
`=> 2[2sinAcos2A][cos^2A−sin^2A] `
`=> 4[sincos^3A−sin^3AcosA]`
=RHS
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