Posted by jazmin on Friday, October 8, 2010 at 8:06am.
can you answer this please about sums and differences of a rational algebraic expression this is the problem 5/x7  x1/x7  2+x/x7 another is x+1/2  x2/3 + 2x1/9 another is 2x+3/3  3x1/2 + x4/12

math  Reiny, Friday, October 8, 2010 at 8:17am
did you mean
5/(x7)  (x1)/(x7)  (2+x)/(x7)
since you already have a common denominator, just add/subtract the numerators
= (5  x + 1  2  x)/(x7)
= (42x)/(x7)
for the second, your common denominator would be the LCM of 2,3, and 9 which would be 18
(x+1)/2  (x2)/3 + (2x1)/9
= [9(x+1)  6(x2) + 2x1 ] /9
= .....
third one is just as easy, the LCD is 12 
correction  math  Reiny, Friday, October 8, 2010 at 10:14am
obviously I have a typo in the second question, should say ...
(x+1)/2  (x2)/3 + (2x1)/18
= [9(x+1)  6(x2) + 2x1 ] /18
= .....