College Algrebra please!?

Question

If f= { (-1,2), (1,3), (2,1), (3,1), (4,2) }

g= { (2,-1), (4,3), (-1,1), (5,4) }, then

f+g=?
Please help me, thank you!

Answer 1

(f+g)(2)=1+(-1)=0 and (f+g)(-1)=2+1=3, can't find the rest based on the information given.

Answer 2

My guess is that you have to add the points (-1,2) and (-1,1) because they have the same x-value to get (-1,3)

Similarly, (2,1) + (2,-1) = (2,0), etc.

For (3,1) since g does not have a value for x=3, assume it's zero, so it remains (3,1). Some textbooks will consider this to undefined.