There is a nice formula for products of cosines, found by multiplying by the complementary products of sines and using the double angle sine formula (as I asked in my question here): $$\prod_{k=1}^n \cos\left(\frac{k\pi}{2n+1}\right)=\frac{1}{2^n}$$
First question: Is there a formula for products of sines of the form $\prod_{k=1}^n \sin\left(\frac{k\pi}{2n+1}\right)$? Or any other interesting formula for products of sines?
Second question, I recently saw on another post here, that there is a formula for the sums of squares of tangents: $$\sum_{k=1}^n \tan^2\left(\frac{k\pi}{2n+1}\right)=2n^2+n$$ How would you prove this formula? From this post here, they use De Moivre's Theorem, root finding and Vieta's formulas, but that seems inefficient when dealing with general $n$ in the above formula.