Posts Tagged ‘week 15’

Week 15 – Adding and Subtracting Rational Expressions

This week we learned how to add and subtract rational expressions. These are a bit harder than multiplying and dividing because the denominator has to be the same throughout the expression.

Steps to simplify:

  1. determine lowest common denominator (LCD)
  2. rewrite each fraction as an equivalent fraction with LCD
  3. Combine numerators by adding/subtracting
  4. reduce if possible

For example: \frac{x-9}{2x}-\frac{3x}{x-4} where “x” cannot equal 0 or 4.

  1. For this expression, the least common denominator would be 2x(x-4) because neither denominator can be simplified any farther or multipled to create a common denominator, so we multiple the two denominators together to create one LCD.
  2. Since we’re multiplying the bottom, we also have to do the same to the top, so the equation becomes: \frac{(x-9)(x-4)}{2x(x-4)}-\frac{(3x)(2x)}{(x-4)(2x)}.
  3. This simplifies to \frac{x^2-13x+36-6x^2}{2x(x-4)}
  4. The final simplified expression will be \frac{-5x^2-13x+36}{2x(x-4)}