Footnote
a In modern algebra, unknown numbers are represented by letters, such as x or y. An example is the equation x + 4 = 6. Subtracting 4 from both sides of the equation reveals that x equals 2.
a In modern algebra, unknown numbers are represented by letters, such as x or y. An example is the equation x + 4 = 6. Subtracting 4 from both sides of the equation reveals that x equals 2.