Answer:
[tex]cos(2x)=\frac{-17}{81}[/tex]
Step-by-step explanation:
First we have to find cosx.
We know that [tex]sin^2x+cos^2x=1[/tex], so it is [tex]cos^2x=1-(7/9)^2=(81-49)/81=32/81[/tex], then we have [tex]cosx=\frac{4\sqrt{2}}{9}[/tex]
Then we have
[tex]cos(2x)=cos^2x-sin^2x=(\frac{4\sqrt{2}}{9})^2-(\frac{7}{9})^2=\frac{32}{81}-\frac{49}{81}=\frac{-17}{81}[/tex]
