因为m是方程x^2-x-4=0的根,所以
m^2-m-4=0
m^2 = m + 4
m^3 = m^2 + 4m = 5m + 4
m^3 + m^2 = 6m+8
m^3 + m^2 -6m -7 = 6m+8 - 6m -7 =1