7.3. Find the number of all integer solutions of the inequality $\sqrt{1+\sin \frac{\pi x}{4}-3 \cos \frac{\pi x}{2}}+\sqrt{6} \cdot \sin \frac{\pi x}{4} \geq 0$, belonging to the interval [1991; 2013].
Answer: 9. Comments. Solution of the inequality: $\frac{2}{3}+8 k \leq x \leq \frac{10}{3}+8 k$. From the given interval, the following numbers will be included in the answer: 1993, 1994, 1995, 2001, 2002, 2003, 2009, 2010, 2011 - 9 numbers.