Which student got the right answer?

Question

Two students worked the following problem. Show your work and circle the correct answer.

 

1/(x-y)+2/(y-x)

 

one got answer a)1/(y-x) the other got answer b)-1/(x-y)

Answer 1

To add the fractions they must have the same denominators.

 

1/(x - y) + 2/(y - x)     multiply second top and bottom by -1

1/(x - y) + -2/-(y - x)

1/(x - y) - 2/(x + y)

(1 - 2)/(x + y)

-1/(x + y)

 

B got the correct simiplication.