Inequality

harpazo

Pure Mathematics
Banned
x^2 - 3x - 18 > 0

( x - 6 ) ( x + 3 ) > 0

x - 6 > 0

x > 6

or

x + 3 > 0

x > -3

This does not seem right.

TheJason

Staff member
Moderator
Looks correct to me.

Last edited:

MarkFL

La Villa Strangiato
Staff member
Moderator
Math Helper
Let's stop at this point in your work:

$$\displaystyle (x-6)(x+3)>0$$

We know the original expression, the quadratic, has a graph that's a parabola opening upwards, so the positive portion of the graph will be to either side of the two roots, thus the solution set is:

$$\displaystyle (-\infty,-3)\,\cup\,(6,\infty)$$

anemone and harpazo

Banned