Question

用列举法表示集合A={[x,y]|x+y=8且xy=15}

Answer 1

x+y=8 (1)
xy=15 (2)
from (1) and (2)
xy=15
x(8-x)=15
x^2-8x+15=0
(x-3)(x-5)=0
x=3 or 5
x=3, y=5
x=5, y=3
(x,y)=(3,5) or (5,3)
A={(x,y)|x+y=8 and xy=15} = { (3,5) , (5,3) }