happy new year
I have this statement: "By quadratic reciprocity there are the integers $a$ and $b$ such that $(a,b)=1$, $(a-1,b)=2$, and all prime $p$ with $p\equiv a$ (mod $b$) splits in $K$ (where $K$ is a real quadratic field)".
I have tried with many properties of quadratic reciprocity but couldn't even get to the first conclusion.
Thank you very much in advance, for any idea or advice for approach the problem