10. (10 points) 42 matchsticks of the same length are arranged as shown in the figure. If each matchstick is considered as a line segment of length 1, then 38 triangles can be counted in the figure. If you want to ensure that no triangles remain in the figure, then at least $\qquad$ matchsticks need to be removed.
【Answer】Solution:
Answer: At least 12 matchsticks need to be removed. Therefore, the answer is: 12.