gaokao 2024 Q4

gaokao · China · national-I_github 5 marks Addition & Double Angle Formulae Addition/Subtraction Formula Evaluation
Given $\cos ( \alpha + \beta ) = m , \tan \alpha \tan \beta = 2$ , then $\cos ( \alpha - \beta ) =$
A. $- 3 m$
B. $- \frac { m } { 3 }$
C. $\frac { m } { 3 }$
D. $3 m$
Given $\cos ( \alpha + \beta ) = m , \tan \alpha \tan \beta = 2$ , then $\cos ( \alpha - \beta ) =$\\
A. $- 3 m$\\
B. $- \frac { m } { 3 }$\\
C. $\frac { m } { 3 }$\\
D. $3 m$