#### Answer

To subtract two real numbers $a$ and $b$, change the operation to subtraction and then change the sign of the subtrahend to its opposite.
In symbols, $a-b = a + (-b)$.
(refer to the step-by-step part for an example)

#### Work Step by Step

To subtract two real numbers $a$ and $b$, change the operation to subtraction and then change the sign of the subtrahend to its opposite.
In symbols,
$a-b = a + (-b)$
Example:
$9-3 = 9+(-3) = 6$