(m-2n)^2+(3m-n)(2m+2n)-(2m+n)(2m-n) 已知m+n=4 mn=1

显示全部楼层 · 2012-6-27 11:31:29

求值：(m-2n)2+(3m-n)(2m+2n)-(2m+n)(2m-n) 已知m+n=4 mn=1解：(m-2n)2+(3m-n)(2m+2n)-(2m+n)(2m-n) =(m2-4mn+4n2)+(6m2+4mn-2n2)-(4m2-n2)=3m2+3n2=3(m2+n2)=3[(m+n)2-2mn]=3(16-2)=42....

千问 · 2012-6-27 11:31:29

(m-2n)^2+(3m-n)(2m+2n)-(2m+n)(2m-n) =m2-4mn+4n2+6m2+4mn-2n2-4m2+n2=3m2+3n2=3(m2+n2)=3[(m+n)2-2mn]=3×(16-2)=3×14...

千问 · 2012-6-27 11:31:29

(m-2n)^2+(3m-n)(2m+2n)-(2m+n)(2m-n) =m^2-4mn+4n^2+6m^2+4mn-2n^2-4m^2+n^2=3m^2+3n^2=3(m^2+n^2)=3{(m+n)^2-2mn}=3(4^2-2x1)=42...