Given $$\arccos(y_1) + \arccos(y_2) + \dots + \arccos(y_k) =kπ$$ for any value of $k>1$ and $$ A= y_1^1 + y_2^2 + \dots + y_{2k}^{2k}, $$ the task is to find the value of $A$.
I have no idea from where should I start with the problem. I tried taking cosine on both sides in first equation but it's not helping.
$$\arccos(y_k)=\sum_{i=1}^k \arccos(y_i)-\sum_{i=1}^{k-1}\arccos(y_i)=k\pi-(k-1)\pi=\pi$$ $$y_k=-1$$ $$A=\sum_{i=1}^{2k}(-1)^i=0$$