xy=9
x+y=-15
x+y=-15
minus x
y=-15-x
sub
x(-15-x)=9
-15x-x^2=9
add 15x+x^2 to both sides
0=x^2+15x+9
quadratic formula
for
0=ax^2+bx+c
x=[tex] \frac{-b+/- \sqrt{b^{2}-4ac} }{2a} [/tex]
0=1x^2+15x+9
a=1
b=15
c=9
x=[tex] \frac{-15+/- \sqrt{15^{2}-4(1)(9)} }{2(1)} [/tex]
x=[tex] \frac{-15+/- \sqrt{225-36} }{2} [/tex]
x=[tex] \frac{-15+/- \sqrt{189} }{2} [/tex]
x=[tex] \frac{-15+/- 3\sqrt{21} }{2} [/tex]
x=[tex] -7.5+/- 1.5\sqrt{21}[/tex]
x=[tex] -7.5+ 1.5\sqrt{21}[/tex] or [tex] -7.5- 1.5\sqrt{21}[/tex]
aprox
x=-0.626136 or -14.3739
those are the 2 numbers
