① When n is on AD, the key is to find PQ. In the right triangle BPQ, BP can be expressed first, then the length of PQ can be obtained according to the degree of ∠QBP ∠, and then the functional relationship between S and T can be obtained according to the area formula of triangle.

② When n is on AB, we still need to find the value of PQ first. We can represent BN first, then BP in the right triangle BNP, and PQ in the right triangle BPQ, so we can get the functional relationship between S and T according to the area formula of the triangle.

(4) It should also be discussed in two situations.

In the first case, when n is on AD, ① when ∠ BMQ = 90, then M and P coincide, so there is BM+ND+FC=BC, that is, 2t+ 1=4, and the value of T can be obtained.

② When ∠ bQM = 90, NQ can be represented by a right triangle NDQ with a length of ND, and then PQ can be represented according to the calculated distance from D to BC. The second method is to represent QM in the right triangle BMQ, then PQ in the right triangle QPM, and then

In the second case, when n is on AB, only ∠ bQM = 90, and the method is the same as ②. The value of t is also obtained by different representations of PQ in the same way as (3) ②. Let me know if you need an answer.