Question

funcao quadratica y=x2-9

Answer 1

y=f(x)

f(x)=x²-9

x²-9=0
x²=9
x=√9
x=±3

Answer 2

veja...

y=x²-9

x² - 9 =0

x² = 9

x=±√9

x=± 3

S={-3,+3}