2. Cut the square into two triangles along the diagonal.

3. Cut one of the triangles into two triangles along the midline, that is, cut the triangles from the middle up and down respectively.

4. Paste the cut triangles on the two blank triangles of the square respectively.

Formula: Clear conclusion: You can finish the ninth question by cutting paper according to the above steps.

Explain the reason: you can cut out a square with paper-cutting and stick the triangle on the two blank triangles of the square to complete the requirements of the ninth question.

Content extension: Pay attention to the position and direction of cutting when paper-cutting, and ensure that the size and shape of the cut triangle are consistent, which requires certain paper-cutting skills and patience.