gaokao 2018 Q4

gaokao · China · national-III-science 5 marks Addition & Double Angle Formulae Direct Double Angle Evaluation
If $\sin \alpha = \frac { 1 } { 3 }$, then $\cos 2 \alpha =$
A. $\frac { 8 } { 9 }$
B. $\frac { 7 } { 9 }$
C. $- \frac { 7 } { 9 }$
D. $- \frac { 8 } { 9 }$
If $\sin \alpha = \frac { 1 } { 3 }$, then $\cos 2 \alpha =$\\
A. $\frac { 8 } { 9 }$\\
B. $\frac { 7 } { 9 }$\\
C. $- \frac { 7 } { 9 }$\\
D. $- \frac { 8 } { 9 }$