Rational expression refers to a fraction in which the numerator and denominator are polynomials.
If you are talking about on Brainly.com it is like this.
To write half write 1/2 (1 forward slash 2)
Answer: 
Step-by-step explanation:
We have given the numbers = 2,0,1,9
We can use addition and subtraction operation to the given numbers such that the answer will be equals to 6.
We can add 2 ,0 and 1 and then subtract from 9 , we will get 6.
So the required expression can be

hence, the required expression can be 