Question
sin2 4˚ + sin2 6˚ +
sin2 8˚ + sin2 10˚ + ……… + sin2 86˚ =?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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