cos(a+b)cos(a-b)=1/5,则(cosa)^2-(sinb)^2=?
已知sina+sinB=1/2,cosa+cosB=1/3,则cos(a-B)=
若cos(a-b)=1/3,则(sina+sinb)^2+(cosa+cosb)^2=
cos^2A - cos^2B + sin^2C=2cosA *sinB *sinC证明
cos^2A - cos^2B + sin^2C=2cosA *sinB *sinC
求证: sina+sinb=2sin[(a+b)/2]cos[(a-b)/2] cosa+cosb=2cos[(a+b)
已知cos(a-b)=3/1,求(sina+sinb)(sina+sinb)+(cosa+cosb)(cosa+cosb
已知cosa+cosb=1/2,sina+sinb=1/3,求cos(a-b)
sin(a-B)cosa-1/2[sin(2a+B)-sinB]=?已知cos(a-π/6)+sina=4√3/5则si
cosa sinb -sin a cos b=s什么?
证明:cos(a+b)=cosa*cosb-sina*sinb
求证:cos(a+b)=cosa*cosb-sina*sinb
已知cosa=1/7,cos(a+B)=-11/14,且a,B均为锐角.求sinB,cos(2a+B)