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，求y的-x方+3xy

的值

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