DOMAIN: Find the domain of the function. In the space provided, type the answer without any spaces between the letters, numbers, or symbols.

Question

Let x and y be directly related. If x is 18 when y is 6, find y when x is 21.

Answer 1

I'm going to assume that "directly related" means a linear relationship. Otherwise, there is no way to write an equation based on the information provided.

Assuming a linear function, use the form y = mx + b. With the information given, m and b cannot be determined. However, the question is simply the domain. For a linear equation, the domain is simply "all real numbers".

In the space provided, type the answer without any spaces between the letters, numbers, or symbols.

I have no idea how that relates to the stated question.......

Answer 2

Hi Lucy S.,

For x and y to be directly related, y is equal to a constant times x, y = k*x, or y/x = k. We can find the constant k with what we've been given. Then we can solve for when x = 21.

y/x = k

6/18 = k

1/3 = k

So we can write this a y/x = 1/3 or y = x/3. And when x = 21:

y = x/3

y = 21/3

y = 7, for x = 21.

The domain is (-∞, ∞).

I hope this helps, Joe.

Answer 3

x and y are directly related. Therefore, y=k*x, where k is the constant that they're directly related by.

You use the given set of x and y to find k:

6=k*18

To solve for k, you divide 18 on both sides, getting k=1/3.

k is a constant, so it's value doesn't change even if y and/or x change. Therefore, you can solve for y by using the equation y=k*x again. Plug in the value we found for k and the (given) value of x that corresponds to the value of y you want to find:

y=(1/3)*21

solve this to get y=7