Question 24119
The domain always refers to the x numbers, and the range always refers to the y numbers.  Now, for the equation 2x+7y = 9, if you are being asked to find the domain and the range, the domain and range are both ALL REAL VALUES.  However, if you are asked to find a few points, then you pick a value of x (that would be a number in the domain!) and PLUG IT IN!  Then you would solve for y, and that would give you a number in the range.  I'm afraid all this domain and range is fine for the mathematicians but it confuses ordinary folks and makes the math seem a lot harder than it really is!!


In this example, you can pick any values for x:
If x =0, then 0+7y = 9, so y = 9/7.
If x = 1, then 2 + 7y = 9, so 7y = 7, y = 1
If y = 0, then 2x + 0 = 9, so x = 9/2

This means that points are like (0, 9/7) or (1,1) or (9/2,0) are all points on this graph:


The graph looks like this if you plot these points:

{{{graph (300,300, -10,10,-10,10, (9-2x)/7)}}}


R^2 at SCC