If you meant:
64.3-3*(2³)/2
That would be 52.3 :)
If I had to simplify 15/24 it would be 5/8
Plotting the points could help you notice that they lie along a parabola. In particular, you can see that
is always 4 more than
.
So, the relation is

If cos(70) = 0.342
the cosine of the alternative angle of 70° will also give the same value
angle measure = 360 - 70 = 240°
cos (240) will also be 0.342