then you will know that cos(2x) = (adjacent)/(hypotenuse)
then use the fact that to find sin(x) and cos(x)
or you could solve.
tan(2x) = -24/7
=> sin(2x)/cos(2x) = -24/7
=> 7 sin(2x) = -24 cos(2x)
and use the double angle formulas to change everything to sine and cosine and continue