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Rational expressions
Getting a common denominator of algebraic fractions
- If you need to add or subtract two rational expressions, work with them in the same way as adding and subtracting normal fractions.
- Firstly find the lowest common denominator (LCD) and make each fraction an equivalent fraction.
- Expand any brackets.
For example:
\begin{eqnarray*}
\frac{x}{x-3} + \frac{5}{x+2}
&=& \frac{x(x+2)+5(x-3)}{(x-3)(x+2)} \\
&=& \frac{x^2+ 2x+5x-15}{x^2 + 2x-3x-6} \\
&=& \frac{x^2 + 7 x - 15}{x^2 - x - 6}
\end{eqnarray*}