Results 1 to 4 of 4

Math Help - Help

  1. #1
    Newbie
    Joined
    Jun 2009
    Posts
    4

    Help

    DETERMINE whether the 2 lines are parallel, perpendicular, or neither.


    9x+2y=-10


    y=-9/2x-6
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member
    Joined
    Mar 2009
    From
    Alberta
    Posts
    173
    Quote Originally Posted by Insignia21 View Post
    DETERMINE whether the 2 lines are parallel, perpendicular, or neither.


    1) 9x+2y=-10


    2) y=-\frac{9}{2}x-6
    Hey Insignia21,

    A good piece of information to know here is that if 2 lines are parallel, they will have the same slope, and if they are perpendicular, the slopes will be negative reciprocals of one another.That said, we can see clearly the the slope of y=-\frac{9}{2}x-6 is m=-\frac{9}{2}. We know this from knowing the formula for a straight line y=mx+b where m=slope

    So we know that for 9x+2y=-10 to be parallel, it must have a slope of m=-\frac{9}{2}, and if it is perpendicular, it must have a slope of m=\frac{2}{9}.

    Now we must solve the first equation for y and find the slope, and then compare it to the above.

    9x+2y=-10

    2y=-10-9x
    y=-5-\frac{9}{5}x
    y=-\frac{9}{5}x-5

    And from this we can see that the slope of
    9x+2y=-10 is m=\frac{9}{5} which when compared above is not the same or the negative reciprocal of the second equation. Therefore the 2 lines are neither parallel or perpendicular.

    Does this help?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor

    Joined
    Apr 2005
    Posts
    15,412
    Thanks
    1328
    Quote Originally Posted by Kasper View Post
    Hey Insignia21,

    A good piece of information to know here is that if 2 lines are parallel, they will have the same slope, and if they are perpendicular, the slopes will be negative reciprocals of one another.That said, we can see clearly the the slope of y=-\frac{9}{2}x-6 is m=-\frac{9}{2}. We know this from knowing the formula for a straight line y=mx+b where m=slope

    So we know that for 9x+2y=-10 to be parallel, it must have a slope of m=-\frac{9}{2}, and if it is perpendicular, it must have a slope of m=\frac{2}{9}.

    Now we must solve the first equation for y and find the slope, and then compare it to the above.

    9x+2y=-10

    2y=-10-9x
    Well done, Kaspar! Up to this point!

    y=-5-\frac{9}{5}x
    y=-\frac{9}{5}x-5
    No, you divide both sides by 2 so this is
    y= -\frac{9}{2}x- 5
    and the slopes are the same!

    And from this we can see that the slope of
    9x+2y=-10 is m=\frac{9}{5} which when compared above is not the same or the negative reciprocal of the second equation. Therefore the 2 lines are neither parallel or perpendicular.

    Does this help?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Member
    Joined
    Mar 2009
    From
    Alberta
    Posts
    173
    Oh dear. Wow. Thanks for that clarification!
    Follow Math Help Forum on Facebook and Google+


/mathhelpforum @mathhelpforum