The range of the sides of a triangle is: first, the sum of the two sides is greater than the third side, and the difference between the two sides is less than the third side. For triangles, the sum of squares of any two sides of an acute triangle is greater than the square of the third side (as long as the sum of squares of two short sides is greater than the square of the long side), and correspondingly, a right triangle is equal to an obtuse triangle, which can be proved by discussing the pros and cons of cosA in the cosine theorem. I hope the landlord will adopt it after playing so much.