Answer: 3x-y = 0
This is equivalent to y = 3x
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Step-by-step explanation:
Rule: Given a line Ax+By = C, the line Bx-Ay = D is perpendicular to it.
The equation x+3y = 9 shows that A = 1, B = 3 and C = 9
Then we can say
Bx-Ay = D
3x-1y = D
3x-y = D
Plug in the coordinates of (1,3) to compute D
3x-y = D
3(1)-3 = D
0 = D
D = 0
Therefore, we go from Bx-Ay = D to 3x-y = 0
If you wanted to solve for y, then you would get y = 3x
The slope of this answer line is 3, and the y intercept is 0.
I recommend using graphing software like Desmos or GeoGebra to confirm the answer.