Exercise 1.8

If we start with an equation, we are allowed to do the same thing to both sides, and we will get another equation which also holds.

Subtracting 4 from both sides gives us

\[ \begin{align}\begin{aligned}3x = 13 - 4\\3x = 9\end{aligned}\end{align} \]

Now we can divide both sides by 3:

\[x = 3\]

So we can choose \(x\) to be \(3\) as a suitable value to illustrate the truth of this statement. In fact \(3\) is the only suitable value in this case. Note, however, that not all equations have exactly one solution: some have zero, some have 2 or more, and some have infinitely many.