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Cos80°Cos35° Cos10°Cos55°

cos80cos35+cos10cos55 =sin10cos35+cos10sin35 =sin(10+35) =sin45 =2/2

cos80cos35+cos10cos55=cos80cos35+sin80sin35=cos80-35㣩=cos45= 2 2 ʴΪ 2 2

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cos35*cos55 =cos35*sin35 =(sin70)/2

sin80cos55+cos80cos35=cos10cos55+sin10sin55=cos55-10㣩=cos45=22ʴΪ 22

sin10cos35+cos10cos55 =sin10cos35+cos10sin35 =sin10+35㣩 =sin45 =2/2

sin35cos55+cos35sin55 =sin35+55 =sin90 =1

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