1.已知(m-1)^2+l6m+3nl=0,求(4m^2-mn-6n^2)-2(m^2-3mn-5n^2)的值

问题描述:

1.已知(m-1)^2+l6m+3nl=0,求(4m^2-mn-6n^2)-2(m^2-3mn-5n^2)的值

(m-1)^2≥0
l6m+3nl≥0
而(m-1)^2+l6m+3nl=0
∴(m-1)^2 =0 l6m+3nl=0
∴m=1
∴n=-2
4m^2-mn-6n^2)-2(m^2-3mn-5n^2=(4*1+2-6*4)-2(4+6-5*4)
=-18-2*(-10)=2