1-1/4sin^2 2A-sin^2B-cos^4Asin(A+B)=3/5sin(A-B)=-4/5

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) 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 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cosA＋cosB＋cosC=1+4sin(A/2)sin(B/2)sin(C/2)证明：cosA＋cosB＋cosC=1+4sin(A/2)sin(B/2)sin(C/2)尽量详细一点选做cosA+cosB+cosC=1+4sin(A/2)sin(B/2)sin(C/2) cos(180-B-C)+cosB+cosC=1+2sin(A/2)[2sin(B/2)sin(C/2)] cos(180-B-C)+cosB+cosC cosA+cos^2A=1,sin^2A+sin^4A+sin^8A (1-sin^6a-cos^6a)/(sin^2a-sin^4a) 三角形ABC中证明 COSA+COSB+COSC=1+4SIN(A/2)*SIN(B/2)*SIN(C/2) 三角形ABC中证明 COSA+COSB+COSC=1+4SIN(A/2)*SIN(B/2)*SIN(C/2) 【证明】Sin A+sin B=2Sin 22 (1-sin^4a-cos^4)/(sin^2a-sin^4a) 化简 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 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), 三角形ABC中,A,B为锐角,sin(A+B)=sinA^2+sinB^2,判断三角形ABC的形状因为 (sin A)^2 +(sin B)^2 =sin (A+B)=sin A cos B +sin B cos A,所以 sin A (sin A -cos B) +sin B (sin B -cos A) =0.(*)又因为 A,B 为锐角,所以 sin A>0,sin B>0.(1) 1:sin(a-b)=sin(-b+a)2:sin(a-b)=sin(-（b-a）),这个为什么是这样的?知识点忘了. 为什么sin-sin^2=1/4 SIN^2 A+SIN^2 B-SIN^2 A*SIN^2 B+COS^2 A*COS^2 b等于 1有谁会啊 教教 求证：sin^2A+sin^2B-sin^2Asin^2B+cos^2Acos^2B=1