Posted by Scotty on .
x2 + 3x  18 < 0
A.(6, 3)
B. (3, 6)
c.(∞, 6)∪(3, ∞)
D. (∞, 3)∪(6, ∞)

Algebra 
Jen,
Find two numbers that multiply to negative 18 and add to 3. (x+6)(x3)

Algebra 
Scotty,
thankyou but, so what would you say the answer is a,b,c or d?

Algebra 
MathMate,
If you sketch the curve f(x) = x²+6x18=0, it will be concave upwards, which means that if the curve cuts the xaxis, the domain of the function f(x)<0 will be between the two roots of f(x)=0. Thus c and d are not appropriate answers.
Jen already factorized f(x)=(x+6)(x3).
You will need to find the value of the roots (where the curve cuts the xaxis) and find the appropriate response.
If you need help understanding the interval notation, please post.