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Easy Math question

  1. Jan 26, 2006 #1
    Find the points where each of the following lines intersects the x and y axes,

    x=6,y=1+6t

    for some reason I don't know how to find the point. If I graph it I understand but I can't work it out.
     
  2. jcsd
  3. Jan 26, 2006 #2
    When you have x = 6, the x-intercept is automatically 6, because x = 6 is just a vertical line, so when y is 0, x must be 6. There is no y-intercept because the line never crosses the y-axis, this is because x cannot = 0.

    What is the t supposed to be in y = 1+6t? A constant (number)? If 't' is a constant then you basically use the same idea.
     
  4. Jan 26, 2006 #3
    Ok I get everything from the beginning, and I know I'm retarded I should have understood that. What is making me confused is the y=1+6t part.

    that comes from the vector equation r=(6,1)+t(0,6)

    Why do you even need to know the y=1+6t part? How do you check from that? I originaly thought you needed to set x or y to zero.....

    BTW thanks
     
  5. Jan 26, 2006 #4
    ok I completely Understand it now....But your explanation aswell as mine is purely based on Logical reasoning. Don't you have to set y=0 to find an x intercept?
     
  6. Jan 26, 2006 #5
    :wink: got it :D
     
  7. Jan 27, 2006 #6

    HallsofIvy

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    Your original post: "Find the points where each of the following lines intersects the x and y axes" implies two different lines. Later you told us this was from r=(6,1)+t(0,6) which is a single line!
    r= (6,1)+ t(0, 6) is the same as the parametric equations x= 6, y= 1+ 6t.

    Since x is always 6, that line does not cross the y-axis. Of course, it crosses the x-axis at (6, 0).

    In general, if you have parametric equations x= a+ bt, y= c+ dt, you find the x-intersept by setting y= 0, solve for t and use that value of t to find x. To find the y-intersept do the opposite: set x= 0, solve that equation for t and use that value of t to find y.
     
  8. Jan 27, 2006 #7
    i just want to say. HallsoftIvy is a very patient and active tutor.

    good work!
     
  9. Jan 27, 2006 #8

    HallsofIvy

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    Who only screams and tears his hair occaisionally.

    The real problem with the internet is that you can't use the two-by-four across the head and shoulders method!
     
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