已知sin^2a+sin^2b+sin^2c=1（a、b、c为锐角）,则cosa*cosb*cosc的最大值高二的不等式题

已知sin(a)=2sin(b)求sin(a/2)/sin(b/2)的值. 3 在三角形ABC中,已知（a2+b2）sin（A-B）=（a2-b2）sin(A+B) 求证：ABC是等腰或直角三角形(a^2+b^2)sin(A-B)=(a^2-b^2)sin(A+B),(sin^A+sin^B)sin(A-B)=(sin^A-sin^B)sin(A+B) sin^A*(sin(A+B)-sin(A-B))=sin^B*(sin(A-B)+sin(A+B)) sin^A*2c 已知3SIN^2A+2SIN^2B=5SINA,求SIN^2A+SIN^2B范围 【证明】Sin A+sin B=2Sin 22 证明sin(a+b)sin(a-b)=sin^2 a-sin^2 b, 求证:sin(a+b)sin(a-b)=sin^2a-sin^2b 已知sin(A)和sin(B)的值,如何求出sin((A+B)/2)的值,谢谢. 已知3sin b=sin(2a+b) 求证tan(a+b)=2tana 已知 3sin A = sin (2B +A ),求证 ： tan（A+B)= 2tanB 懂得进.证明,sina+sin(a+b)+sin(a+2b)+...sin(a+nb)=sin(a+ab/2)sin[(n+1)b/2]/sin(b/2) 三角形ABC中,已知（sin^2 A-sin^2 B-sin^2 C)/(sinB sinC)=1 求A? 已知sinA=1/5,求2sin(A+B)cosA-sin(2A+B) 已知sin(A+B)=2/3,sin(A-B)=1/5.求tanA/tanB 已知sin(a+b)=1/2,sin（a-b)=1/3,求tana/tanb 证明sina sin(a+2b) - sinb sin(b+2a) =sin(a+b)sin(a-b) 化简（sin(a-b)-2sin a cos b）/2sin a sin b +coa(a+b) 已知3sin^2a+2sin^2b-2sina=0,则y=sin^2a+sin^2b的最大值? 关于三角函数的问题 已知3sin^2a+2sin^b=2sina,求sin^2a+sin^b的取值范围