Analysis: Let the trapezoid height be X, D be the origin, DC be the Y axis, and DA be the X axis as the rectangular coordinate system. Then a (2,0), B( 1, x), p (0 0,y) and then the vector pa+3pb = (5 5,3x-4y). Find the square of the vector module =25+(3x-4y)(3x-4y)

For such a formula, it is obvious that when 3x=4y, the square term is 0, and the original formula takes the minimum value of 25, that is, the minimum value of the module is 5.

Because the symbols are difficult to type, the square is written as a product? Sorry)