simultaneous equations(EASY)

xy =10 ----------- 1
3x-2y+4=0 ----------- 2

from 1
x=10/y ----------3

sub 3 into 1

3(10/y)-2y+4 = 0
30/y-2y+4 = 0
-2y²+4y+30=0
y²-2y-15=0
(y+3)(y-5)=0
y+3=0 or y-5=0
y=-3 or y=5

sub y=-3 into 3
x=10/-3 = -10/3

sub y=5 into 3
x=10/5


therefore the roots are (x = -10/3, y = -3) and (x=2, y=5)


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checking

x = -10/3, y = -3
(-10/3)(-3)=10 and
(-10/3)(3)-(2)(-3)+4 = -10+6+4 =0

x = 5/3, y = 5
(2)(5) = 10 and
(3)(2)-(2)(5)+4 = 6-10+4 = 0

2008-06-03 02:12:01 補充：
計到最後時漏打了一行 sorry
x=10/5
x=2