Finding y using points and slope

phoenixrebel

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Oct 2, 2010
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I am not sure if I'm doing this right:
The line through A (2,4) and B (3,y) is perpendicular to a line with slope 1/9. Find y.

I started by using point A and the negative reciprocal of 1/9, which is -9 to write the equation of the line in slope-intercept form- 4=-9(2) + b, then solved for b and got b=22.

Then used the same formula to solve point B:
y=-9(3)+22---> y=-5

Is that correct?
 

tkhunny

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You tell us. Find a way to check your result. I might recommend finding the equation of a line through (3,-5) with a slope of -9 and seeing if you can get to (2,4). If so, you are done.
 

phoenixrebel

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Oct 2, 2010
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I hope this is right:

I graphed the line y=-9x+22, then checked to see if points A and B were on that line. They were. So, the answer y=-5 is correct. Can you offer confirmation?
 

Denis

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Feb 17, 2004
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phoenixrebel said:
I hope this is right:
I graphed the line y=-9x+22, then checked to see if points A and B were on that line. They were. So, the answer y=-5 is correct. Can you offer confirmation?
Keep it simple:
Since y = -9x + 22, then 9x + y = 22
Substitute (2,4): 18 + 4 = 22
Substitute (3,-5): 27 - 5 = 22
 

phoenixrebel

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Thank you!
 
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