Question

If f(x)=x+7and g(x)=1/x-13, what is the domain of (f•g)(x)

Answer 1

Answer:

(-∞, 0)∪(0, ∞)

Step-by-step explanation:

You are given the functions f(x) and g(x).  Now, you have to find (f*g)(x).  To do this, you have to multiply the two functions.

f(x) = x + 7

g(x) = 1/x - 13

(f*g)(x) = (x + 7)(1/x - 13)

(f*g)(x) = -13x + 7/x + 1 - 91

(f*g)(x) = -13x + 7/x - 90

The domain has to include all of the x-values that will produce a rational number.  So, look at where the x's are locate

-13x:  You could put any rational number into this value and still have a rational number.

7/x:  For this value, you cannot have 0 as an x-value.  Every other number is fine.

This means that the domain will be (-∞, 0)∪(0, ∞).  

You use parentheses and not brackets for the zero side because you don't want to include zero in the domain, but you do want to include all of the other numbers around zero.  There are no brackets on the infinity side because infinity isn't a number.  The ∪ symbol is used to combine domains.

Answer 2

Answer: 7x-90/x-13

Step-by-step explanation:

f(x)= x+7

g(x)=1/x-13

(f•g)(x)=1/x+13+7

1+7(x-13)/x-13

1+7x-91/x-13

7x-90/x-13