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怎样计算sin15°加sin75°的值

sin15°+sin75° =2sin[(15°+75°)/2]cos[(15°-75°)/2] =2sin45°cos(-60°) =2sin45°cos60° =2×(√2/2)×(1/2) =√2/2

和差化积公式: sin15°+sin75° =2sin[(15°+75°)/2]cos[(15°-75°)/2] =2sin45°cos(-30°) =2sin45°cos30° =2×(√2/2)×(√3/2) =√6/2 或者sin15°+sin75° =sin(45°-30°)+sin(45°+30°) =(sin45°cos30°-sin30°cos45°)+(sin45°cos30°+sin30°cos45°...

sin15º+sin75º =sin75º+sin15º =sin75º+cos75º =√2(√2/2sin75º+√2/2cos75º) =√2(sin75ºcos45º+cos75ºsin45º) =√2*sin120º =√6/2

sinαsinβ=-[cos(α+β)-cos(α-β)]/2

sin15sin30sin75 =(1/2)sin15sin(90-15) =(1/2)sin15cos15 =(1/2)*[(1/2)*2sin15cos15] =(1/4)sin30 =1/8

15度看成45-30度,75看成40+30度,105看成60+45度,再根据sin (a+b)=sinacosb+cos asinb,(a和b代表角度),中间加号可以替换成减号

解:sin75°+sin15° =2sin((75°+15°)/2)cos((75°-15°)/2) (应用和差化积公式) =2sin45°cos30° =2(√2/2)(√3/2) =√6/2。

sin15°cos75° =(根号6-根号2)/4X(根号6+根号2)/4 =[(根号6-根号2)X(根号6+根号2)]/16 =(6-2)/16 =1/4

sin15° =sin(45°-30°) =sin45°cos30°-cos45°sin30° =(根号6-根号2)/4 sin75° =sin(30°+45°) =1/2 x 根号2/2 +根号3/2 x 根号2/2 = (根号2+根号6)/4

有没有看到两个度数的和与差分别是90度和60度,利用这个关系,特殊角

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