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Homework Help: Can someone tell me what I did?

  1. Oct 15, 2017 #1
    1. The problem statement, all variables and given/known data
    I got two equations of a line a1x + b1y + c1 =0 and a2x + b2y + c2 =0 they multiplied both and said gave a quadratic staying it represents a system of lines. it's a big quadratic(in x and y) with a lot of coefficients and right below it they said it intersects at some blah point (a, b) where a and b are functions of the coefficients of the quadratic. I tried to prove this by saying the point of intersection will give you the maximum value of y and x in the quadratic. to do this i total diffeitated (not partial) wrt x and then wrt y and set the dy/dx and dx/dy to 0, then I and got 2 linear equations i solved it and got the right answer (a, b) .

    I have no idea what i just did : |

    2. Relevant equations

    3. The attempt at a solution
    to convince myself that the maximum value of y this really is the case i took y= m1x + c1 and y = m2x+c2 corresponding to the above a1x+b1y + c1 and a2x + b2y+c2 and multiplied it getting y^2 = m1m2x^2 + x(m1c2+m2c1) + c1c2. differtiation with respect to y and setting it do 0 does not give me the point of intersection : (

    what on earth is going on?!

    *Usually I see partial differtial equations for maximizing 2 variables (no idea how that works either) but this is total? why is it working? what's even happening?
    * If the first form gives me the right answer, why not with y = mx +c?
    *general case wot.jpg

    pic attached is the problematic nonsense. second pic is two equations arrived after differtiation and solving by crammer's to get the right answer (in the corner)

    Attached Files:

  2. jcsd
  3. Oct 15, 2017 #2


    Staff: Mentor

    Thread closed.

    Please post a new thread, clearly stating the problem you're trying to solve, and showing your work.
    The image you posted with the problem is oriented sideways, with a few illegible scrawls along the side. The other image is hard to read, and doesn't give any indication of what you are trying to do.
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