`3x + 7 = 4t - 3`

and

`7x(7+1) - 3t(5-12x)`

Okay, so what is different about the above and why does it matter?

Answer: One you can **solve**, and one you can **manipulate **(such as simplify).

A really good way (and the way I use) to remember is that equations have an equals (**=**) sign.

3x**=**5 -> “3 x **equals **5″.

With an equation, we seek a solution set (if it exists). Expressions, however, are something you can manipulate.

**Equations **we solve, **expressions **we manipulate.