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75的余弦值

cos(45+30) =cos45sin30-cos30sin45 =2分之根号2 * 1/2 - 2分之根号3 * 2分之根号2 =(根号2-根号6)/4 sin(45+30) =sin45*sin30+cos45*cos30 =2分之根号2 * 1/2 + 2分之根号2 * 2分之根号3 =(根号2+根号6)/4 tan(45+30) =sin75/cos75 =(根号2+根号6)/(根号2-根号6)

作Rt三角形ABC,角C为90度,角A为30度.延长CA到D使AD=AB.所以,角D=角DBA=15度,角CBD=75度.所以,AB=AD根据勾股定理得:BD=根号下CD平方+BC平方. 所以:sin75=CD/BD=(根号6+根号2)/4 ,cos75=BC/BD=(根号6-根号2)/4 ,tan75=BD/BC=2+根号3.

sin75°=(√6+√2)/4 cos75°=(√6-√2)/4

用(30°+45°)算.拆了答案就出来了

正弦:30度是二分之一45度是二分之根号二60度是二分之根号三53度是零点八 余弦:30度是二分之根号三45度是二分之根号二60度是二分之一53度是零点六 正切:30度是三分之根号三45度是一60度是根号三53度是三分之四

cos(45+30)=cos45sin30-cos30sin45=2分之根号2 * 1/2 - 2分之根号3 * 2分之根号2=(根号2-根号6)/4sin(45+30)=sin45*sin30+cos45*cos30=2分之根号2 * 1/2 + 2分之根号2 * 2分之根号3=(根号2+根号6)/4tan(45+30)=sin75/cos75=(根号2+根号6)/(根号2-根号6)

sin75度=cos15度=sin(45+30)=sin45cos30+sin30cos45=(√6+√2)/4;cos75度=sin15度=cos(45+30)=cos45cos30-sin45sin30=(√6-√2)/4tan75度=1/tan15度=sin75度/cos75度=2+√3.

sin75°=sin30°+45° =sin30°cos45°+cos30°sin45° =1/2√2/2+√3/2√2/2 =√2/4+√6/4 =√6+√2/4 cos75°=cos30°+45° = cos30°cos45°-sin30°sin45° =√3/2√2/2-1/2√2/2 =√6-√2/4 tan75°=sin75°/cos75° =√6+√2/√6-√2 =2+√3

sin75=sin(30+45)=sin30cos45-cos30sin45=(根号2-根号6)/4cos75=cos30cos45+sin30sin45=(根号2+根号6)/4

4分之根号6减根号2

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