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Brie's question from Facebook (finding equation of perpendicular line)

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Jameson

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Jan 26, 2012
4,043
Brie writes:
Hi everyone! I need a little help with finding a perpendicular line using an ordered pair and the equation to the previous line.

The equation is y= 3x+3 and the ordered pair is (1,1).

So far, I've used the slope-point equation to come up with such:

y-y1=m(x-x1)
y-1= -1/3(x-1)
y=(-1/3)(x)-(-1/3)(1)+1
At the end I ended up getting:
y=(-1/3)x+(1/3)+1
y=(-1/3)x+(4/3)

When I graph it, it's not going through the point (1,1) which it should. What am I doing wrong?

Thank you!
 
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Jameson

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Jan 26, 2012
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Re: Brian's question from Facebook (finding equation of perpendicular line)

Hi Brie, (Wave)

You have solved the problem correctly actually! :) When you plug-in x=1 to your final equation you get \(\displaystyle y=-\frac{1}{3}(1)+\frac{4}{3}=\frac{4}{3}-\frac{1}{3}=\frac{3}{3}=1\), so $y=1$ like we want it to.

If you graph it as well you can see the right angle it forms. What device are you using to graph the equation? Perhaps there is a small error with inputting the equation.

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