sin a =2/√5,a=几°

sin a =2/√5,a=几° sin角a=0.9928 角a是几 sin(2π+a) ,sin(π+a),sin(5π+a) 的区别为什么sin(2π+a) =sina sin(π+a)=-sina 已知sin a+cos a= -1/5 求1）sin acos a 2）sin a-cos a 求证1+sin a+cos a+2sin acos a/1+sin a+cos a=sin a+cos a sin(arccos(2sin(a)))= 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 sin 2a+2sin方a/ 1+tan a =2sin a cos a 求证:sin 2a/1+sin a+cos a=sin a+cos a-1急 tan a =3求4sin a-2cos a/5cos+3sin a 【证明】Sin A+sin B=2Sin 22 已知3SIN^2A+2SIN^2B=5SINA,求SIN^2A+SIN^2B范围 sin（-19π/6）=?已知[3Sin(π+a)+Cos(π-a)]/4Sin(-a)-Sin(5π/2+a)=2，求tan a (cos a)^4+(sin a)^2*(sin a)^2+(sin a)^2=? cosA+cos^2A=1,sin^2A+sin^4A+sin^8A sin²20°+sin80°sin40°且sin(a+b)sin(a-b)=sin^2a-sin^2b 已知sin(a)=2sin(b)求sin(a/2)/sin(b/2)的值.