宸茬煡sin(蟮+a)=-1/2锛屽垯cos伪=?急

在△ABC中,求证；sin^(A/2)+sin^(B/2)+sin^(C/2)=1-2sin(A/2)sin(B/2)sin(C/2） 三角形ABC中,已知（sin^2 A-sin^2 B-sin^2 C)/(sinB sinC)=1 求A? 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 在三角形ABC中sin^A+sin^B=2sin^C,则角C为? 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) 在△ABC中,求证sin²A+sin²B+sin²C=2(1+cosAcosBcosC） 已知(sin A)^2+(sin B)^2+（sin C)^2=1,且A,B,C均为锐角,求cos Acos Bcos C的最大值 sin^2 A=sin^2 B+sinBsinC+sin^2 C 求A角 Rt三角形中 角c等于九十度 求证 sin^2A?tanA+sin^2B?tanB=1-2sin^2A?sin^2B/cosA?cosB 已知tan(A-B)/tanA+sin^2C/sin^2A=1,求证：tanA*tanB=tan^2C 知tan(A-B)/tanA+sin^2C/sin^2A=1求证tanAtanB=tan^2C 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 在三角形ABC中,设sin^2(A/2)+2sin^2(B/2)+sin^2(C/2)=1求tan(A/2)*tan(C/2) 已知A+b+C=π 求证 cosA+cosB+cosC=1+4sin(A/2)sin(B/2)sin(C/2) △ABC中,sin^2A+sin^2C-sin^2B+sinAsinC=0(1)求B（2）求(a+c)/b的取值范围 判断三角形形状（高中）(1)a^+b^+c^=2倍根号3absinC(2)Sin^A+Sin^B+Sin^C>2 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))