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2Cos10 sin70

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...

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=sin10*1/2*cos40*cos20 =1/2*2sin10cos10cos20cos40/(2cos10) =1/2*sin20cos20cos40/(2cos10) =1/2*sin40cos40/(4cos10) =1/2*sin80/(8cos10) =1/2*cos10/(8cos10) =1/16

原式=sin10cos40cps20 =2sin10cos10cos20cos40/2cos10 =sin20cos20cos40/2cos10 =2sin20cos20cos40/4cos10 =sin40cos40/4cos10 =sin80/8cos10 =sin80/8sin80 =1/8

sin10sin50sin70 =2cos10sin10sin50sin70/(2cos10) =sin20*cos20*cos40/(2cos10) =sin40*cos40/(4cos10) =sin80/(8cos10) =cos10/(8cos10) =1/8

:(2cos10º-sin20º)/sin70° =[2cos10º-sin(30º-10º)]/sin70º =[2cos10º-(sin30ºcos10º-cos30ºsin10º)]/sin70º =(2cos10º-(1/2)cos10º+(√3/2)sin10º)/sin70º =...

原式=(sin5°/cos5°-cos5°-sin5°)sin20°/(1+cos20°) =-(2cos10°/sin10°)sin20°/(2cos²10°) =-4(cos²10°sin10°)/(2cos²10°sin10°) =-2.

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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