Question

A função f(x)=-x2+9x-18 corta o eixo x em:
a)x'=1 e x"=1
b)x'=3 e x"=6
c)x'-3 e x"=5
d)x'=1 e x"=-3

Answer 1

-x² + 9x -18 = 0 ===> *(-1)

x² -9x +18= 0
(x -3) . (x -6) = 0
(x -3) = 0 ==> x'=3 ✓
(x -6) = 0 ==> x"=6 ✓

por Bhaskara:
∆= (-9)² -4.1.18= 81-72=9 =>√∆=3
x = -(-9)±√∆/2a
x = 9±3/2
x' = 9-3/2= 6/2 =3 ✓
x" = 9+3/2= 12/2= 6✓