To add and subtract rational expressions, or any kind of fraction, we need to have exactly the same denominator. In order to find a common denominator in these examples, we need to multiply one fraction by a clever form of one. It's always a good idea to factor the denominators to see if they have common factors. The least common denominator will make reducing easier later, but even if you use a different common denominator, you can still get the correct answer with some additional work. If the original problem was subtraction, you need to be very precise with how you distribute the negative. Combine like terms in your new numerator, factor if possible, and reduce if possible.
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