f(x) = cos²x + cos²(x+Ï/3 )
= 1/2cos(2x)+1/2 + 1/2cos(2x+2Ï/3) +1/2
= 1/2{ cos2x+cos(2x+2Ï/3) } +1
= 1/2{ cos2x+cos2xcos2Ï/3-sin2xsin2Ï/3 } +1
= 1/2{ cos2x-1/2cos2x-â3/2sin2x } +1
= 1/2{ 1/2cos2x-â3/2sin2x } +1
= 1/2{ cos2xcosÏ/3-sin2xsinÏ/3 } +1
= 1/2cos(2x+Ï/3) + 1
æå°æ£å¨æ T = 2Ï/2 = Ï
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