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If a=b cos((2pi)/3)= c cos((4pi)/3), the...

If `a=b cos((2pi)/3)= c cos((4pi)/3),` then write the value o `a b+b c+c a`

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We know that ,
`cos(2pi)/3​=(−1)/2​`
`cos(4pi)/3=(−1)/2`
Given `a=bcos(2pi)/3=c cos(4pi)/3`​
=`a=b(−1/2)=c(−1/2)`
...
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