As an old man who took the college entrance examination eight years ago, let the side length of triangle ABC be X and the volume be Y, and then take the range of X from 0 to 5 with the root number 3. So if you equilateral triangle ABC, your area can be calculated, which is almost 3/4 x of the root sign? . Then the height, OF=5cm, and then subtract the vertical distance from O to AB. I'm too lazy to forget how much, but it's not difficult anyway. Next, calculate the volume formula of the triangular pyramid, and then calculate the maximum value according to the range of X. I remember it seems to be based on the derivative, I forgot, hehe.