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共回答了17个问题采纳率:100% 举报
MN = 1 = √3sinA - cosA = 2sin(A - π/6) = 1 ,sin(A - π/6) = 1/2 ,
(A - π/6) = π/6 或 5π/6 ,A = π/3 或 π ,但A是三角形内角 ,故A=π/3 ,
2)
1 + sin2B = (sinB)^2 + (cosB)^2 + 2·sinB·cosB = (sinB + cosB)^2
因此:-3 = (1+SIN2B)/(COSB的平方-SINB的平方)
= (sinB + cosB)^2 / [(cosB)^2 - (sinB)^2]
= (cosB + sinB)/(cosB - sinB)(分子分母同时除以cosB)
= (1 + tanB)/(1 - tanB)
即:3tanB - 3 = 1 + tanB , 解得tanB = 2
1年前
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