This problem belongs to piecewise function, which can be done in junior high school. It is estimated that there are two situations to do the first.

That is, △PQR is completely within the triangle △ABC. At this time, the overlapping part is the area of △PQR, and △ ∠A = 30° Let AP = X.

You can get the bottom pq of △PQR = x/2. The height here is 3 times X/4 of the root number, so the area Y= 3 times x the square of the root number/16. At this time, the value range of x is 0 < x < 5.

Focus on the second case, because it is not easy to draw. Take your time and look at the value of x at this time. five

You can get Y= (- root number 3 times the square of x+15 times root number 3 times X-50 times root number 3 )/2. It's really difficult to type out ordinary forms by yourself (5