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若tan(a+b)=2tana,求证:3sinb=sin(2a+b)
人气:403 ℃ 时间:2020-01-30 14:44:47
解答
tan(A+B)=2tanAsin(A+B)/cos(A+B)=2sinA/cosAsin(A+B)*cosA=2sinA*cos(A+B) sin(A+B)*cosA-sinA*cos(A+B)=sinA*cos(A+B)sinB=sinA*cos(A+B)sin(2A+B)=sin(A+B)*cosA+sinA*cos(A+B)=3sinA*cos(A+B)3sinB=sin(2A+B)
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