sin 10 sin 30 sin 50 sin 70
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Solution Sin10*sin30*sin50*sin70 = sin10* 1 2 *sin50*sin70 = 1 2 * (sin10*sin50) * sin70 = 1 4 * (2 sin10*sin50) * sin70 = 1 4 * (cos (50-10)-cos (50+10)) * sin70 ( using Cos (A-B) - Cos (A+B) = 2SinA SinB ) = 1 4 * (cos40 - cos60) * sin70 = 1 4 * (cos40-1/2) * sin70 = 1 4 cos40 sin70 - 1 8 sin70 = 1 8 * (2 cos40 sin70) - 1 8 sin70 trailer fast furious 10
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