Question

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$Cos²10+Cos²20+Cos²30+Cos²40+Cos²50+Cos²60+Cos²70+Cos²80+Cos²90 =$

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Answer 1

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Answer 2

QUESTION:-

Cos²10 + Cos²20 + Cos²30 + Cos²40 + Cos²50 + Cos²60 + Cos²70 + Cos²80 + Cos²90 =

ANSWER:-

USING THE FORMULA:-

$cos0 = sin(90 - 0)$

$= {cos}^{2} 10 + {cos}^{2} 20 + {cos}^{2} 30 + {cos}^{2} 40 + {sin}^{2} 40 + {sin}^{2} 30 + {sin}^{2} 20 + {sin}^{2} 10 + 0$

$= ( {cos}^{2} 10 + {sin}^{2} 10) + ( {cos}^{2} 20 + {sin}^{2} 20) + ( {cos}^{2} 30 + {sin}^{2} 30) + ( {cos}^{2} 40 + {sin}^{2} 40)$

NOW:-

USING

${cos}^{2} 0 + {sin}^{2} 0 = 1$

$1 + 1 + 1 + 1$

$= 4$