You may want to review quadratic equations first.

To solve a quadratic inequality, you get everything on the
left-hand side, so the right-hand side is just 0. Try to make it
so the leading coefficient is positive (you might have to rewrite
the inequality, or multiply both sides by −1). Now there are
three cases. If the discriminant is negative, then the side with
the variables is *always* positive, so the solution is
either all real numbers or nothing, depending on which way the
inequality goes. If the discriminant is positive, then the
equation (if we pretend the inequality is an equals sign for a
moment) has two real solutions. For example, if the left-hand side
were *x*^{2} − 8*x* + 15, the solutions
would be 3 and 5. Now you just have to learn the rules. If it's a
less-than sign, the answer is (3, 5). If it's a less-than-or-equal
sign, the answer is [3, 5]. If it's a greater-than sign, the
answer is (−∞, 3) ∪ (5, ∞). Finally, if it's a
greater-than-or-equal sign, the answer is (−∞, 3] ∪ [5,
∞).

That covers two cases. The third is trickier. Suppose the
discriminant is 0. Then the equation would have one real solution.
For example, if the left-hand side were *x*^{2} +
2*x* + 1, the solution would be −1. Then if it's a
less-than sign, there's no solution. If it's a less-than-or-equal
sign, the answer is just −1. (You can write this as an
interval like this: [−1, −1].) If it's a greater-than
sign, the answer is all numbers *except* for −1, so
you write (−∞, −1) ∪ (−1, ∞).
Finally, if it's a greater-than-or-equal sign, the answer is all
real numbers.