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Im trying to determine the y and x intercepts of this line.

  1. Apr 20, 2016 #1
    1. The problem statement, all variables and given/known data
    I am trying to determine the x- and y-intercepts of the line 3x – 5y + 15 = 0.

    2. Relevant equations
    standard form

    3. The attempt at a solution:

    To find the x-intercept (where the line crosses the x-axis), substitute 0 in for y:
    3x + 5y + 15 = 0 (substituted 0 in for y)
    3x + 5(0) + 15 = 0 (multiply 5 by 0)
    3x + 15 = 0 (Next ,subtract 15 from both sides)
    3x = -15 (divided both sides by 3)
    x = -5
    x-intercept = -5.


    I will use this method to solve for the y-intercept.


    To find the y-intercept (where the line crosses the y-axis), substitute 0 in for x:
    3x + 5y + 15 = 0 (substituted 0 in for x)
    3(0) + 5y + 15 = 0 (multiply 3 by 0)
    5y + 15 = 0 (Next ,subtract 15 from both sides)
    5y = -15 (divided both sides by 5)
    y = -3
    y-intercept = -3


    I'm pretty sure I did it correct but i just want to be sure I understand what I'm doing and answering it correctly. Also can you guys tell me if my way is like clear, as in you can understand it. Thx alot :)
     
  2. jcsd
  3. Apr 20, 2016 #2

    Math_QED

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    It seems correct, but why do you substitute? Do you understand that?
     
  4. Apr 20, 2016 #3
    Sorry what do you mean by bold?
     
  5. Apr 20, 2016 #4

    Math_QED

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    Nothing, was just a code error. Could you answer the question so I can see whether you understand why you can do this to solve the exercice?
     
  6. Apr 20, 2016 #5
    Well my dad kinda just taught me this way, so you would try to isolate the variable y( you can start with x but im starting with y). so to isolate the variable i have to move some values to the other side of the equations. I searched online and it said i should substitute the variable y for 0. I don't know why but i did ( my dad didnt tell me to do that i did it on my own). So I did and continue the way my dad taught me and got my final result.
     
  7. Apr 20, 2016 #6

    Math_QED

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    Wel you can consider it this way. The y-axe has equation: x = 0, so this are all the points with x coordinate 0. You want to know where your line intersects with the y-axis, and you know that the x-coordinate should be 0. Since you say x = 0 in the equation, you will automatically get the y value corresponding with this x-value. Is this clear? (I need to go to school now btw, so I won't reply for a couple of hours)
     
  8. Apr 20, 2016 #7
    Wow that really helps thanks alot ill keep that in mind while i answer my next problem :)

    thx you !!!
     
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