The following is the answer process:

pq=kmn

p+q=k(m+n)，

There is a positive real number pq, which is equivalent to the discriminant (p-q)? =k？ (m+n)？ -4 kmn & gt； =0。

K is obviously greater than 0, so the above formula is equivalent to k & gt=4mn/(m+n)? =4/(m/n+n/m+2)

This formula needs to hold for all MnS, so we only look at the maximum value of 4/(m/n+n/m+2).

m/n+n/m & gt； =2√(m/n*n/m)=2, so 4/(m/n+n/m+2)

Therefore, k>= 1.