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6. 1-sin 10° sin 50° sin 70°虱丽(al 1/8hi 3/9 |
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Answer» 1- sin10 sin50 sin 70= 1 - {(2sin10cos10)sin50cos20}/2cos10 = 1 - 2sin20cos20cos40/4cos10 = 1 - 2 sin40cos40/8cos10 = 1 - 2sin80/8cos10= 1 - cos10/8cos10 = 1 - 1/8= 7/8 thanks |
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