已知m^2-mn=21,mn-n^2=-15,求代数式:3m^2-5mn+2n^2的值_数学解答

已知m^2-mn=21,mn-n^2=-15,求代数式:3m^2-5mn+2n^2的值

人气：123 ℃　时间：2019-09-27 20:22:31

解答

m^2-mn=21 (1)
mn-n^2=-15 (2)
(1)×3-(2)×2
3m^2-3mn-2mn+2n^2=63+30
3m^2-5mn+2n^2=93