Answer:
They most have common denominators.
Step-by-step explanation:
Let the following two rational expressions:
![\frac{p}{a} , \frac{q}{b}](https://tex.z-dn.net/?f=%5Cfrac%7Bp%7D%7Ba%7D%20%20%2C%20%5Cfrac%7Bq%7D%7Bb%7D)
where p,a,q, b are integers, a and b the denominators are not 0, i.e. ![a,b\neq 0](https://tex.z-dn.net/?f=a%2Cb%5Cneq%200)
We can add rational expressions only if their denominator is same.
That is why we find LCD to be
.
Then,
![\frac{p}{a} +\frac{q}{b} =\frac{pb+qa}{ab}](https://tex.z-dn.net/?f=%5Cfrac%7Bp%7D%7Ba%7D%20%2B%5Cfrac%7Bq%7D%7Bb%7D%20%3D%5Cfrac%7Bpb%2Bqa%7D%7Bab%7D)
Let the following two rational expressions:
![\frac{p}{a} , \frac{q}{b}](https://tex.z-dn.net/?f=%5Cfrac%7Bp%7D%7Ba%7D%20%20%2C%20%5Cfrac%7Bq%7D%7Bb%7D)
where p,a,q, b are integers, a and b the denominators are not 0, i.e. ![a,b\neq 0](https://tex.z-dn.net/?f=a%2Cb%5Cneq%200)
We can add rational expressions only if their denominator is same.
That is why we find LCD to be
.
Then,
![\frac{p}{a} +\frac{q}{b} =\frac{pb+qa}{ab}](https://tex.z-dn.net/?f=%5Cfrac%7Bp%7D%7Ba%7D%20%2B%5Cfrac%7Bq%7D%7Bb%7D%20%3D%5Cfrac%7Bpb%2Bqa%7D%7Bab%7D)
So, the correct answer is the last option that we can sum rational expressions if they have common denominator.