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Prove that: cos^2A+cos^2(A+pi/3)+cos^2(A...

Prove that: `cos^2A+cos^2(A+pi/3)+cos^2(A-pi/3)=3/2`

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`cos^2A+cos^2(A+pi/3)+cos^2(A-pi/3)`
we know that :--
`=>cos2A=2cos^2A-1`
`=>cos^2A=(cos2A+1)/2`
so question becomes:-
`=>(cos2A+1)/2+(cos(2A+(2pi)/3)+1)/2+(cos(2A-(2pi)/3)+1)/2`
taking `1/2` common and bringing all `1` in one side we have,
...
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