Prove that `5costheta+3cos(theta+pi/3)+3` lies between `-4a n d10.`

Explanation

Given,

`5costheta+3(costhetacos60^o−sinthetasin60^o)+3`

`=1/2​[13costheta−3sqrt(3)
​sintheta]+3`

Put `13=rcosalpha,3sqrt(3)
​=rsinalpha`

`so,r=sqrt(169+27)`

`​=sqrt(196)`

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