sin阝=1/3,sin(a+阝)=1,求sin(2a+3阝)

sin阝=1/3,sin(a+阝)=1,求sin(2a+3阝) 1-sin a+sin a的平方-sin a的立方+……若a是正锐角,且sin a-cos a=0.5,求1-sin a+sin^2a-sin^3a+…… 求证:sin a (1+cos2a)=sin a cos a 求证1+sin a+cos a+2sin acos a/1+sin a+cos a=sin a+cos a 证明恒等式tan a*sin a/tan a-sin a=1+cos a/sin a 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) 求证:sin 2a/1+sin a+cos a=sin a+cos a-1急 sin 2a+2sin方a/ 1+tan a =2sin a cos a 8sin(45+a)sin(45-a)=1,sin^4a-cos^4a= cosA+cos^2A=1,sin^2A+sin^4A+sin^8A 在△ABC中,求证；sin^(A/2)+sin^(B/2)+sin^(C/2)=1-2sin(A/2)sin(B/2)sin(C/2） 证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2证明 sin^2A+sin^2B-sin^2A*sin^2B+cos^2A*cos^2B=1 sin((3π)/3-a)=sin(π+(1/2-a))=-(sin(1/2-a))＝-cosa 3sin(a)^2+2sin(b)^2=1,3sin(a)=2sin(b),a,b都为锐角,求a+2b的值是3sin(2a)=2sin(2b), 已知 sin a-cos a=1/2,则 sin^3 a-cos^3 a 已知tan a=2 求 sin平方a－3sin a×cos a+1 a/sinα=a+1/3sinα-4sin^3α=a+2/2sinαcosα  1）在三角形PF1F2中 由正弦公式|F1F2|/sin∠F1PF2=|PF1|/sin∠PF2F1=|PF2|/sin∠PF1F2然后是如何推得|F1F2|/sin∠F1PF2=（|PF1|+|PF2|）/（sin∠PF2F1+sin∠PF1F2）的?2）sin 3a/(sin a+sin 2a)=[3sin a-4(sin a)^3]/(sina+2sin a*cos a)