If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

# Adding & subtracting rational expressions: like denominators

Sal adds 6/(2x²-7) + (-3x-8)/(2x²-7) and subtracts (9x²+3)/(14x²-9) - (-3x²+5)/(14x²-9).

## Want to join the conversation?

• Can you simplify this any further:

2Y+7 all over 2Y

I would assume that you can't since the +7 is in the numerator but I'm not extremely confident
• You are correct... you can't simplify any further. The +7 is preventing any further reduction. We can only cancel factors (items being multiplied). Since the numerator contains addition, it prevents us from cancelling.
• In the second problem,why do we distribute a negative sign and why do we distribute? If we do it the first method as well,will we get the same answer as distributing?
• you distribute the negative sign because you are subtracting. If you don't distribute then you would be adding.
(1 vote)
• Given a rational expression, identify the excluded values by finding the zeroes of the denominator.
• square root of 20/x^2 + square root of 5/4x^2 =
• Its simple you just have to add the 2 2y's and leave the seven, See Simple.
• At , why can't you simplify 12x^2 and 14x^2 by 2 to be 6x^2 - 2 / 4x^2 - 9?
• No, we can't simplify any further. When we reduce fractions we cancel out common factors (items being multiplied. For example: 10/15 = 2/3 because 10 = 2*5 and 15 = 3*5 and they share a common factor of 5. In the video, 12x^2 and 14x^2 are terms (they are being added/subtracted with other values). We can't cancel terms.
Hope this helps.
• what is the product of 5^4 and 5^4
• These two objects have the same base. So when you multiply them, you can add the exponents. 5^4×5^4=5^(4+4)=5^8.
• On video at why is it -2-3x and not -3x-2 instead? Many thanks in advance.
• The 2 expressions are equivalent. "-3x-2" would be preferred as it is in standard form. But, it isn't required.
• How about if we have like numerators, do we take the common factor too?
• When adding/subtracting all fractions, we need a common denominator. There is no requirement to have a common numerator.