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The angle between two lines

  • 18-01-2015 9:59pm
    #1
    Take Your Pants Off
    Registered Users, Registered Users 2 Posts: 1,519 ✭✭✭


    I cannot figure out how to do this question even from using the example on the previous page of the questions.
    find the obtuse angle between the lines x-2y-1=0 and 3x-y+2=0


Comments

  • #2
    Daniel2590
    Registered Users, Registered Users 2 Posts: 1,645 ✭✭✭Daniel2590


    Basically you want to find the slope of each line and then use the formula tan∅ = ± (m1-m2)/(1+m1m2). Angle is 135° :)


  • #3
    Peregrine
    Moderators, Education Moderators Posts: 26,403 Mod ✭✭✭✭Peregrine


    Damn you, Dan. I had the whole thing typed up in LaTeX code and everything :(


  • #4
    Take Your Pants Off
    Registered Users, Registered Users 2 Posts: 1,519 ✭✭✭Take Your Pants Off


    Thank you so much for an amazing fast reply.
    and Nim thank you too ! :)


  • #5
    Daniel2590
    Registered Users, Registered Users 2 Posts: 1,645 ✭✭✭Daniel2590


    Nim wrote: »
    Damn you, Dan. I had the whole thing typed up in LaTeX code and everything :(

    Haha the one time I actually visit this forum :pac:


  • #6
    Peregrine
    Moderators, Education Moderators Posts: 26,403 Mod ✭✭✭✭Peregrine


    Be careful with perpendicular lines. The product of the slopes of two perpendicular lines is -1, so the denominator becomes 0..and you don't wanna go there.

    If you don't realise they're perpendicular from the slopes, a 0 denominator should tell you.


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