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Linear Graph Line

  • Thread starter thomas49th
  • Start date
  • #1
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Homework Statement


The line l has equation y = 3x + 4
Cans someone xplain how [tex]y = -\frac{1}{3}x-4[/tex] is perpendicular to line l(bisects l at 90°)

Homework Equations



y = mx + c
 
Last edited:

Answers and Replies

  • #2
cristo
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What condition must the gradients of two perpendicular lines satisfy?
 
  • #3
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negtive gradient.

y = mx + c where m is a negitive number?
 
  • #4
HallsofIvy
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No, remember that the slope of a line is the tangent of the angle the line makes with the x-axis. If two lines are y= m1x+ b and y= m2x+ c, then the two lines are parallel if and only if m1= m2 and parallel if and only if (m1)(m2)= -1.

Those can both be derived from properties of the tangent function.
 
  • #5
cristo
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and parallel if and only if (m1)(m2)= -1.
Just correcting a typo: you mean perpendicular if and only if (m1)(m2)= -1.
 
  • #6
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perpendicular if and only if (m1)(m2)= -1.
cant it be

perpendicular if and only if (m1)(m2)= -0.5? Or any other number there? Was that just an example? If not what is so special about -1?

(m1)(m2)= -1
so 3 * -1/3 = -1

cheerz, Big help
 
  • #7
Integral
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Graph a set of perpendicular intersecting lines.

Now using the graphs, compute the slopes, can you now see why the relationship is [itex] m_1 m_2 = -1 [/itex]

You may need to look at several sets of lines to see the relationships.
 
  • #8
HallsofIvy
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Thomas49th, are you saying you cannot read our responses?
 
  • #9
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aha, ingenius. It works. Thanks a load :cool:
 

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