Quadratic extension

A quadratic extension is a field extension $𝐿 : 𝐾$ of degree $[𝐿 : 𝐾] = 2$ . ring Hence $𝐿 = 𝐾 [\sqrt 𝑑]$ for some squarefree $𝑑 \in 𝐾$ . In particular, a quadratic extension of $ℚ$ is called a Quadratic field.