[![enter image description here][1]][1] [1]: https://i.sstatic.net/usHbi.png I don't really understand how to approach this problem. I know that $w=\sum_{n=1}^{N}{a_ny_nx_n}$ and $y_n(w^T*x_n+b)=1. $ So I can solve for $b$ from that equation but I can't figure out how to apply equation(1) that I'm supposed to use.