10. On the coordinate plane, depict the set of points $(a, b)$ such that the system of equations $\left\{\begin{array}{c}x^{2}+y^{2}=a^{2}, \\ x+y=b\end{array}\right.$ has at least one solution.
Answer. $|b| \leq \sqrt{2}|a|$.

Criteria. «士» the set of parameters $a$ and $b$ is correctly found, but it is not plotted on the coordinate plane; «Ғ» the answer is correct for $a>0$, but not for $a<0$.