Question

已知|2m-5|+(2m-5n+20)的2次方=0,求（-2m的2次方）-2m（5n-2m)+3n(6m-5n)-3n(4m-5n)的值.

拜托各位哩~~~

Answer 1

已知，|2m-5|+(2m-5n+20)^2 = 0 ，且绝对值和平方值都大于等于0，
可得：2m-5 = 0 ，2m-5n+20 = 0 ，
解得：m = 5/2 ，n = 5 。

(-2m)^2-2m(5n-2m)+3n(6m-5n)-3n(4m-5n)
= 4m^2-10mn+4m^2+18mn-15n^2-12mn+15n^2
= 8m^2-4mn
= 4m(2m-n)
= 0