m-2的绝对值+(2m-5n+1)^2=0
m-2=0
2m-5n＋1=0
所以
m=2
n=1
所以
（-2m)^2-2m(5n+2m)+3n(3m-2n)
=4m²-10mn-4m²＋9mn-6n²
=-mn-6n²
=-2×1-6×1²
=-2-6
=-8