1. (Suzhou City) If for any pair of real numbers $x, y$ that are not both zero, we have $f(x, y)=5 x^{2}+8 x y+3 y^{2}+\lambda\left(x^{2}+y^{2}\right)>0$, then the range of values for $\lambda$ is $\qquad$
1. $(\sqrt{17}-4,+\infty)$.