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# I need help by tomorrow-I tried something but it shows as wrong answer

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Find the value of B-A if the graph of Ax+By=3 passes through the point (-7, 2) and is parallel to the graph of x+3y=-5

Sep 9, 2021

#1
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From x + 3y = -5, y = -x/3 - 5, so the slope of the line is -1/3. The slope of the new line is also -1/3, so y = -x/3 + B.  Pugging in x = 2 and y = -7, we get -7 = -2/3 + B, so B = -19/3.

Then the line is y = -x/3 - 19/3.  Then 3y = -x - 19, so 3y + x = -19.  We want the right-hand side to be 3, so we mutiply both sides by -3/19: -9/19*y - 3/19*x = 3.  Therefore, B - A = -19/3 - 3 = -28/3.

Sep 9, 2021
#2
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It still says its wrong... I don't understand

Sep 9, 2021
#3
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Rewrite the equations as:

y = -(A/B)x + 3/B and  y = -(1/3)x - 5/3

The values multiplying the x term constitute the slope.

Parallel lines have the same slope, so  A/B = 1/3  or  B = 3A

Since the first line passes through (-7, 2) we must have  2 = -(A/B)*(-7) + 3/B  or  2 = -(A/3A)*(-7) + 3/(3A)  or  2 = 7/3 + 1/A

Rearrange this last equation to find A, then find B (from B = 3A), then you can find B-A.

Sep 10, 2021
edited by Alan  Sep 10, 2021