Question

若tanAtanB=三分之根号三,求（2-cos2A)(2-cos2B)的值

Answer 1

用万能公式：

（2-cos2A)(2-cos2B)

=(2-(1-tan^2A)/(1+tan^2A)) (2-(1-tan^2B)/(1+tan^2B))

=(1+3tan^2A)(1+3tan^2B)/(1+tan^2A)(1+tan^2B)

=(4+3tan^2A+3tan^2B)/(4/3+tan^A+tan^2B)

=3

我抄的