am+bn=1与cm-dn=-2两边分别相加,得(a+c)m+(b-d)n=-1,或2(a+c)m+2(b-d)n=-2.a(2x-y)+b(x+2y)=2与 c(2x-y)+d(x+2y)=-4两边分别相加,得(a+c)(2x-y)+(b-d)(x+2y)=-2.比较：2x-y=2m=10,x+2y=2n=-6,解得：x=14/5,y=-22/5....