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2Cos10 sin70

sin20=sin(30-10) 所以 (2cos10°—sin20°)/sin70° =(2cos10°—sin(30-10))/sin70° =(2cos10-(sin30cos10-cos30sin10))/sin70 =(2cos10-1/2cos10+根号3/2sin10)/sin70 =(3/2sin10+根号3/2sin10)/sin70 =根号3(根号3/2cos10+1/2sin10)/sin70 =根...

即在花简计算用到 sin20=sin(30-10) 所以 (2cos10°—sin20°)/sin70° =(2cos10°—sin(30-10))/sin70° =(2cos10-(sin30cos10-cos30sin10))/sin70 =(2cos10-1/2cos10+根号3/2sin10)/sin70 =(3/2sin10+根号3/2sin10)/sin70 =根号3(根号3/2cos10+1/2...

原式= (2cos10-sin20)/sin70 =(2cos10-sin20)/cos20 =[cos10+(cos10-cos70)]/cos20 =[cos10+2sin40*sin30]/cos20 =[cos10+2*1/2*sin40]/cos20 =[cos10+cos50]/cos20 =2cos30*cos20/cos20 =2cos30 = 根号3

sin20=sin(30-10) 所以 (2cos10°—sin20°)/sin70° =(2cos10°—sin(30-10))/sin70° =(2cos10-(sin30cos10-cos30sin10))/sin70 =(2cos10-1/2cos10+根号3/2sin10)/sin70 =(3/2sin10+根号3/2sin10)/sin70 =根号3(根号3/2cos10+1/2sin10)/sin70 =根...

即在花简计算用到 sin20=sin(30-10) 所以 (2cos10°—sin20°)/sin70° =(2cos10°—sin(30-10))/sin70° =(2cos10-(sin30cos10-cos30sin10))/sin70 =(2cos10-1/2cos10+根号3/2sin10)/sin70 =(3/2sin10+根号3/2sin10)/sin70 =根号3(根号3/2cos10+1/2...

sin20=sin(30-10) 所以 (2cos10°—sin20°)/sin70° =(2cos10°—sin(30-10))/sin70° =(2cos10-(sin30cos10-cos30sin10))/sin70 =(2cos10-1/2cos10+根号3/2sin10)/sin70 =(3/2sin10+根号3/2sin10)/sin70 =根号3(根号3/2cos10+1/2sin10)/sin70 =根...

应该是(2cos10°-sin20°)/cos20° (2cos10°-sin20°)/cos20° =[2cos(30°-20°)-sin20°]/cos20° =(2cos30°cos20°+2sin30°sin20°-sin20°)/cos20° =(√3cos20°+sin20°-sin20°)/cos20° =√3

因为30度的sin和cos 都是常数 式子里都是20度 化成常数和统一的度数好计算

解答: 题目有误。 (3-sin70°)/(2-cos²10°) =(3-cos20°)/[2-(1+cos20°)/2] =2(3-cos20°)/(4-1-cos20°) =2(3-cos20°)/(3-cos20°) =2

原式=(sin5/cos5-cos5/sin5)cos70/(1+sin70) =[(sin5)^2-(cos5)^2]/sin5/cos5*cos70/(1+sin70) =-2cos10/sin10*sin20/(1+sin70) =-2cos10/sin10*sin10*cos10/(1+sin70) =-2*(1+cos20)/(1+sin70) =-2

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