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    Question

    sin2 4˚ + sin2 6˚ +

    sin2 8˚ + sin2 10˚ + ……… + sin2 86˚ =?
    A 23 Correct Answer Incorrect Answer
    B 21 Correct Answer Incorrect Answer
    C 30 Correct Answer Incorrect Answer
    D 24 Correct Answer Incorrect Answer

    Solution

    sin 2 4˚ + sin 2 6˚ + sin 2 8˚ + sin 2 10˚ + ……… + sin 2 86˚ = (sin2 4˚ + sin2 86˚)+(sin2 6˚ + sin2 84˚) + .…. + (sin2 44˚ + sin2 46˚) = (sin2 4˚ + cos2 4˚)+(sin2 6˚ + cos2 6˚) + .…. + (sin2 44˚ + co2 44˚)  {As sin (90˚ - θ) = cos θ} = (1)+(1) + .…. upto 21 times { As sin2 θ + cos2 θ= 1} = 21 ` ` ` ` ` ` ` ` ` ` ` `

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