Solve the following simultaneous equations.

1. x^2 + y^2 = 25--------1
3x - 4y +25 = 0-----------2
from2
3x - 4y +25 = 0
(3x+25)/4 = y----3
put3 into 1
x^2+[(3x+25)/4]^2=25
(16x^2+9x^2+150x+625)/16=25
25x^2+150x+625-400=0
x^2+6x+9=0
(x+3)^2=0
x=-3
put x=-3into3
[3(-3)+25]/4=y
y=4


2.) x^2 + y^2 + 3x +2y = -2 -----1
2x - 3y = 2--------2
from2
2x-3y=2
x=(2+3y)/2------3
put 3 into 1
[(2+3y)/2]^2+y^2+3[(2+3y)/2]+2y=-2
(4+12y+9y^2)/4+y^2+(6+9y)/2+2y+2=0
4+12y+9y^2+4y^2+12+18y+8y+8=0
13y^2+38y+24=0
(13y+12)(y+2)=0
y=-2or-12/13
put y=-2andy=-12/13into3
x=[2+3(-2)]/2 or x=[2+3(-12/13)]/2
x=-4or x=-31/13


唔得閒做住....一陣再做sor-0-
希望你睇得明la~~

2006-12-16 08:49:45 補充：
3.) 2x^2 - 3xy - 2y^2 - 12 = 0------1-2x + 3y + 4 = 0 -------2from2-2x + 3y + 4 = 0(3y+4)/2=x-----3put 3 into 12[(3y+4)/2]^2 - 3y(3y+4)/2 - 2y^2 - 12 = 0(9y^2+24y+16)-9y-12y-4y^2-24=09y^2-4y^2+24y-12y-9y+16-24=05y^2+3y-8=0(5y+8)(y-1)=0y=-8/5or1

2006-12-16 08:50:05 補充：
puty=-8/5 or 1into3[3(-8/5)+4]/2=x or[3(1)+4]/2=xx=-2/5 or x=3.5