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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...

=(2cos10-2sin10cos10)/cos20 =2cos10(1-sin10)/cos20 =2sin80(sin90-sin10)/cos20 =2sin80(2cos50sin40)/cos20 =8sin20cos50sin80 =4(2sin80cos50)sin20 =4(sin130-sin30)sin20 =4(cos40-sin30)sin20 =4cos40sin20-2sin20 =2(sin60-sin(-20))-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

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...

原是=(2cos(30-20)°-sin20°)/sin70°= 孤独的......根号三

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

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

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

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