Respostas

2014-06-08T23:07:43-03:00
Olá, Lailakethelen!

x² - 3x - 18 = 0
a = 1
b = -3
c = -18

Δ = b² - 4.a.c
Δ = (-3)² - 4.1.(-18)
Δ = 9 + 72
Δ = 81

-b +- √Δ / 2.a
-(-3) +- √81 / 2.1
3 +- 9 / 2

x' = 3+9/2 = 12/2 = 6
x'' = 3-9/2 = -6/2 = -3
2014-06-08T23:09:21-03:00
Só usar a fórmula de Bháscara 
X= -b±√Δ 
Considerando que delta =  b²-4.a.c

x²-3x-18=0 
delta= 9+72= 81
x=[3+-9]/2 
x'=6 
x''=-3 
1 5 1