Question

求代数式的值(1)已知M方+m-1=0,求m的立方+2m方-2005的值 （2）已知x方+y方-4x+y+4又4/1=0

Answer 1

(1)m^2+m=1

m^3+2m^2-2005

=m(m^2+2m)-2005

=m(m^2+m+m)-2005

=m(1+m)-2005

=m^2+m-2005

=1-2005

=-2004

(2)x^2+y^2-4x+y+4+1/4=0

配方得到,(x-2)^2+(y+1/2)^2=0

∴x=2 y=-1/2

∴y的-x方+3xy

=(-1/2)的-2次方+3×2×(-1/2)

=4-3

=1