Rationalizing the denominator, simply means "getting rid of that pesky root at the bottom", and we do so by simply multiplying it by something to take it out, of course, we multiply the bottom, we have to also multiply the top,

Answer:
The GCF is going to be 20
Step-by-step explanation:
This Is how I find the GCF of 2 numbers. I find the prime factorization first, then I find the common factors and multiply them. Here
The prime factorization of 20, 2 × 2 × 5= 20
The prime factorization of 80, 2 × 2 × 2 × 2 × 5 = 80
The common factors are 2, 2, and 5. We multiply those to get the GCF.
2 × 2 × 5 = 20
F: R -> R, f(x) = ax + b;
f(1) = 8 => a + b = 8;
f(2) = 14 => 2a + b = 14 => a = 6 and b =2;
f(3) = 20 => 6*3 + 2 = 20 True;
f(4) = 26 => 4*6 + 2 = 26 True;
then, f:R -> R, f(x) = 6x + 2;