You might want to simplify the equation first. Basically, we'll use y = ax+b instead.
[tex]-7x-2y=-21\\-2y=-21+7x\\y=\frac{-21}{-2}+\frac{7x}{-2} \\y=\frac{21}{2}-\frac{7x}{2}\\y=\frac{21-7x}{2}[/tex]
Should have been like this then you are able to graph.
To graph, you need to find the x-intercept and y-intercept.
(1) Find x-intercept, substitute y = 0
[tex]0=\frac{21-7x}{2} \\0=21-7x\\7x=21\\x=3[/tex]
Thus, the graph has a x-intercept at (3,0). For those who are wondering where does the fractional 2 go, just multiply the whole equation by 2 to get rid of the fraction.
(2) Find y-intercept, substitute x = 0
[tex]y=\frac{21-7x}{2}\\ y=\frac{21-0}{2}\\ y=\frac{21}{2} \\[/tex]
Also 21/2 = 10.5, Thus the graph passes y-axis at (0, 10.5)
Now plot the graph, make a line from x-intercept and y-intercept and you should get like this (Picture below.)
