# Inequality

### 1st degree inequality

A first degree inequality is solved like an ordinary equation. The only difference is that when dividing or multiplying an equation by a negative number, the sign of the inequality turns, i.e. its direction changes. This can be seen below with the example on the right.

**Example 1**

### Quadratic inequality

A quadratic inequality does not work in exactly the same way. A quadratic inequality is always solved with the corresponding equation.

**Example 2**

The zeros of the quadratic equation are* x = -3* and* x = 3*. The graph is a upward opening parabola

The graph runs below the *x*-axis between the zeros. Then the solution of the inequality is

**Example 3**

When does the values of function *f *are negative?

Zeros

Graph

The values are negative when x < -4 and x > 1

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