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Math Help - find the equation of the line...perpendicular to....

  1. #1
    Junior Member
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    Unhappy find the equation of the line...perpendicular to....

    the question says==> find an equation of the line through (-1,3) which is perpendicular to 4x+3y=12


    and i got this===> y=-4/3x+b ==> i flip the -4/3 to 3/4

    then putting it all together i got ==> 3= 3/4 (-1) + b

    but thats as far as i can go.. i don't reall know what else to do (im not good with fractions)

    how would i multiply the fraction and add it with whole number?

    (there is a thread tht is something like this already and i posted in it, bc i didn't wanted to start a new one, but i guess i can)

    Thanks ,
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  2. #2
    MHF Contributor
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    Quote Originally Posted by Candy101 View Post
    the question says==> find an equation of the line through (-1,3) which is perpendicular to 4x+3y=12


    and i got this===> y=-4/3x+b ==> i flip the -4/3 to 3/4

    then putting it all together i got ==> 3= 3/4 (-1) + b

    but thats as far as i can go.. i don't reall know what else to do (im not good with fractions)

    how would i multiply the fraction and add it with whole number?

    (there is a thread tht is something like this already and i posted in it, bc i didn't wanted to start a new one, but i guess i can)

    Thanks ,
    Rearrange 4x+3y=12 to y=-\frac{4}{3}x+4

    m=-4/3

    the gradient of the line perpendicular to this is 3/4

    then we know this line passes through (-1,3)

    using this formula y-y_1=m(x-x_1)

    y-3=frac{3}{4}(x+1)

    simplify it .
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