=m^2+(n- 1)m+(n- 1)^2- 1

=m^2+(n- 1)m+ 1/4(n- 1)^2+3/4(n- 1)^2- 1？

=[m+ 1/2(n- 1)]^2+3/4(n- 1)^2- 1

When n= 1; The minimum value of M=0 is-1.

I was so careless just now. Why is the-1 behind your formula missing?

How did this come about, even with the following-1? . .

Your step size is already equal to (n- 1) 2. How can you turn it into something hard?

Your thinking is right, but when sorting out the formula, I feel that you are very complicated. . . . For such a problem, it is best to use an alternative method, for example, setting (n- 1) to t. ...

Take a look at my steps to solve the problem, refer to it, and see the differences between our two ideas. . . .