求证：(a^2/sin^2 x )+(b^2/cos^2 x)大于等于a+b)^2快

求证:sin(a+b)sin(a-b)=sin^2a-sin^2b 求证数学题,在三角形ABC中,求证sin^2(A)+sin^2(B)+sin^2(C) 求证：(a^2/sin^2 x )+(b^2/cos^2 x)大于等于a+b)^2快 求证(a^2+b^2-c^2)/(b^2+c^2-a^2)=(sin(A+B)+sin(A-B))/(sin(A+B)-sin(A-B)) 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 sin^2A+sin^2B=sin^2C求证△ABC的形状 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 设A,B为锐角,且sin^2A+sin^B=sin(A+B),求证A+B＝90sin^2A+sin^2B=sin(A+B)sin^2A表示sinA的平方 在△ABC中,求证；sin^(A/2)+sin^(B/2)+sin^(C/2)=1-2sin(A/2)sin(B/2)sin(C/2） 求证sin(a+b)sin(a-b)=sina^2-cosb^2 求证：sin(a+b)cosa-(1/2)[sin(2a+b)-sinb]=sinb 求证cos2a-cos2b=-2sin（a+b）sin（a-b） 1/2（cos2A-cos2B）=sin(A+B)sin(A-B）求证 求证cosa*sinb=1/2[sin(a+b)-sin(a-b)] 求证sin与tan 已知3sinB=sin(2A+B),求证tan(A+B)=2tanA 求证：sin^2A+sin^2B-sin^2Asin^2B+cos^2Acos^2B=1 求证 sin的4次方x减去cos4次方a等于2sin平方a-1