sina+sinb=a,cosa+cosb=b,ab不等于0,cos(a-b)等于
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求证:cos(a+b)=cosa*cosb-sina*sinb
证明:cos(a+b)=cosa×cosb-sina×sinb
已知cos(a-b)=3/1,求(sina+sinb)(sina+sinb)+(cosa+cosb)(cosa+cosb)=
若sina+sinb=1,cosa+cosb=o求cos^2a+cos^2b
sina+sinb=a,cosa+cosb=b,ab不等于0,cos(a-b)等于
sin(a+b)cos(a-b)=sina*cosa+sinb*cosb
求证:sin(a+b)cos(a-b)=sina*cosa+sinb*cosb麻烦个位 帮个忙~
sinA(cos(2A+B)+cosB)=cosA(sin(2A+B)-sinB)证明
证明下列恒等式:sin(a+b)*cos(a-b)=sina*cosa+sinb*cosb
cos(A+B)+sin(A-B)=(cosA+sinA)(cosB-sinB)
cos(A-B)-sin(A+B)=(cosA-sinA)(cosB-sinB).
已知sina+sinb+siny=0,cosa+cosb+cosy=0,则cos(a-b)=?
已知sina+sinB=1/2,cosa+cosB=1/3,则cos(a-B)=
sina+sinb=1/4 cosa+cosb=1/3 则cos(a-b)=
若sina+sinb+sinr=0,cosa+cosb+cosr=0,则cos(a-b)=?
sina+sinb=1,cosa+cosb=0,求cos(a+b)=?
已知sina+sinb=siny,cosa+cosb=cosy,求证cos(a-y)=1/2
已知cosa+cosb=1/2,sina+sinb=1/3,求cos(a-b)rt.