1. **Problem statement:** We have a square with a triangle inside it formed by a diagonal. The triangle has angles 45° and 70°, and we need to find the unknown angle $x$ inside the triangle. 2. **Recall the rule:** The sum of the interior angles of any triangle is always 180°. 3. **Apply the rule:** Let the three angles of the triangle be 45°, 70°, and $x$. Then, $$45° + 70° + x = 180°$$ 4. **Solve for $x$:** $$x = 180° - 45° - 70°$$ $$x = 65°$$ 5. **Conclusion:** The unknown angle $x$ inside the triangle is 65°.