# what is x and y in this equation

7x+9y-28

You did not post an equation. An equation must include an equals sign. Did you mean to post 7x + 9y = 28?

I am going to write an answer assuming you meant 7x + 9y = 28.

Without a second independent equation that uses one or both of these variables, you cannot solve for a single set of values. But you can solve for all values of x with respect to y or all values of y with respect to x.

7x + 9y = 28 (subtract 9y from both sides of the equation)

7x = -9y + 28 (divide both sides of the equation by 7)

x = -(9/7)y + 4

You now have a solution set for all values of x with respect to y

(x, -(9/7)y + 4)

You can select values for y and solve for x to have a definite solution set, but there is an infinite number of solution sets. Example:

Let y = 7/9

x = -(9/7)(7/9) + 4 = -1 + 4 = 3

So (3, 7/9) is a solution set. Try these two numbers in the original equation.

7(3) + 9(7/9) = 28

21 + 7 = 28

This equation is true, so (3, 7/9) is a solution set.

You can illustrate all solution sets with a linear graph by solving for y with respect to x.

7x + 9y = 28 (subtract 7x from both sides of the equation then divide both sides by 9)

y = (-7/9)x + 28/9

This is the y-intercept form of a linear equation. Its slope is -7/9 and its y-intercept is 28/9. A graph of the line illustrates all solutions for the given equation.
answered Mar 2, 2014 by Inquisitive Expert (21,460 points)