已知m=99又1/2,n=50又1/4,求代数式(2m-n)^2-(3m-n)(m-n)-4n^2的值
问题描述:
已知m=99又1/2,n=50又1/4,求代数式(2m-n)^2-(3m-n)(m-n)-4n^2的值
答
解
(2m-n)^2-(3m-n)(m-n)-4n^2
=(4m^2-4mn+n^2)-(3m^2-4mn+n^2)-4n^2
=4m^2-4mn+n^2-3m^2+4mn-n^2-4n^2
=m^2-4n^2
=(m+2n)(m-2n)
=200*(-4)
=-800