Answer:
Step-by-step explanation:
If you read through the bottom paragraph, you see it concludes with, "the equations describe the same line." This means the system has infinite solutions, because the two lines intersect everywhere.
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The rest of the solution is described in the paragraph. Starting with the rearranged form
-ax +ay +9a = 0
"subtract 9a from both sides" means you now have ...
-ax +ay +9a -9a = 0 -9a
or
-ax +ay = -9a . . . . . . . . "-9" goes in the first box
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Now, dividing by -a gives you ...
(-ax)/(-a) +(ay)/(-a) + (-9a)/(-a)
x - y = 9 . . . . . . . . . . . . "9" goes in the second box, confirmed by the following statement that the equations (this, and x - y = 9) "describe the same line".
