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Thread: Two equations with two variables

  1. #1
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    Two equations with two variables

    8xy = 2x + 21y
    3xy2= 2x + 15y

    I want to find the x and y

    Answers :

    x= 3
    y = 2
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  2. #2
    MHF Contributor

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    Re: Two equations with two variables

    Multiply the first equation by 5: 40xy= 10x+ 105y
    Multiply the second equation by 7: 21xy^2= 14x+ 105y
    Subtract: 40xy- 21xy^2= -4x

    If x is not 0, divide by x: 40y- 21y^2= -4 or 21y^2- 40y- 4= 0. Solve that using the quadratic formula for y, then solve for x. That gives x= 3, y= 2 and another solution.

    If x is 0 then y= 0. x= y= 0 is a third solution.
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