Get image dimension after rotation

Question

I asked this question at StackOverflow, maybe because it's all about math, I don't get a working solution.

I'm actually trying to get the image dimension after rotation using canvas with a certain angle in Javascript.

Answer 1

$200 \cos(30^\circ) + 80 \sin (30^\circ) $ by $200 \sin(30^\circ) + 80 \cos (30^\circ) $ .

$\cos(30^\circ) = \frac{\sqrt{3}}{2}$ while $\sin(30^\circ) = \frac{1}{2}$.