The question:
The function p is defined by $-2|x+4|+10$. Solve the equality $p(x) > -4$
Here were my steps to solving this:
1.) Subtract 10 from both sides -> $-2|x+4| > -14$
2.) Divide both sides by -2 -> $|x+4|>7$
3.) $x+4$ should therefore be 7 units or greater from zero on the number line, meaning either greater than 7 or less than -7:
$x+4 > 7$
$x+4 < -7$
4.) Subtract 4 from both sides:
$x > 3$
$x < -11$
Graphing this, I see my signs are the wrong way round but I'm not quite sure where I've gone wrong.
$20$ is greater than $8$, right?
$$20 > 8$$
Now divide both sides by $-2$:
$$-10 > -4$$
Whoops! That's not right. This is because when you multiply or divide an inequality by a negative number, you must change the sense of the inequality: $>$ becomes $<$, and $\le$ becomes $\ge$ etc:
$$-10 < -4$$