Inequalities and rearranging formulae

Solving an inequality

Treat it exactly like an equation, with one exception: if you multiply or divide by a negative number, the inequality sign flips. $-2x>6$ gives $x<-3$, not $x>-3$. Checking one value from your answer set is the fastest way to catch a flipped sign.

Showing the solution

On a number line, an open circle means the value is not included ($<$ or $>$) and a filled circle means it is ($\le$ or $\ge$). For integer solutions, list them: for $-2

Rearranging a formula

To make $r$ the subject of $A=\pi r^2$: divide both sides by $\pi$, then take the square root. Do the operations in the reverse order to how they were applied — the same idea as undoing an equation, just with letters.