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Math Help - Finding a line perpendicular to another line

  1. #1
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    Question Finding a line perpendicular to another line

    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?
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  2. #2
    Senior Member Stroodle's Avatar
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    You can use the formula y-y_1=m(x-x_1)

    So if you sub in the point (-1,3) and use m=\frac{3}{4} you get:

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

    y=\frac{3}{4}x+\frac{15}{4}
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  3. #3
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    Quote Originally Posted by Stroodle View Post
    You can use the formula y-y_1=m(x-x_1)

    So if you sub in the point (-1,3) and use m=\frac{3}{4} you get:

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

    y=\frac{3}{4}x+\frac{15}{4}

    how did you get 15/4?
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  4. #4
    Senior Member Stroodle's Avatar
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    y-3=\frac{3}{4}(x+1)

    y-3=\frac{3}{4}x+\frac{3}{4}

    y=\frac{3}{4}x+\frac{3}{4}+3

    y=\frac{3}{4}x+\frac{3}{4}+\frac{12}{4}

    y=\frac{3}{4}x+\frac{15}{4}
    Last edited by mr fantastic; December 13th 2009 at 05:05 AM. Reason: Removed a comment that is no longer necessary.
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