1.

`[5cos theta+3cos(theta+pi/3)+3]` lies between (A) 4 and 10 (B) -4 and 10 (C) -10 and 4 (D) None of the above

Answer» `3cos(theta+pi/3)=3{costhetacospi/3-sinthetasinpi/3}`
`=3costheta*1/2-3sinthetasqrt3/2`
`=3/2costheta-3sqrt3/2sintheta`
`5costheta+3cos(theta+pi/3)+3`
`=5costheta+3/2costheta=3sqrt3/2sintheta+3`
`=1/2(13costheta-3sqrt3sintheta)+3`
`=sqrt(169+27)/2*cos(theta+phi)+3`
`=sqrt196/2cos(theta+phi)+3`
`=7cos(theta+phi)+3`
`-4<=7cos(theta+phi)+3<=10`
option c is correct.


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