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Maths Question (Simultaneous Equations), Help needed

  • 18-04-2014 4:26pm
    #1
    PKdude
    Registered Users Posts: 101 ✭✭


    Hi, I've been trying to do this maths question for a while now and I've had no luck, I don't know how to do it. It's Simultaneous Equations which I'm usually good at. Here it is:

    2r - s = 10
    rs - s(to the power of 2) = 12


Comments

  • #2
    Peregrine
    Moderators, Education Moderators Posts: 26,403 Mod ✭✭✭✭Peregrine


    Substitute one into the other. More specifically, substitute the linear equation into curve/circle.

    [latex]
    2r = 10 + S[/latex]

    [latex]r = 5 + \frac{S}{2}
    [/latex]


    [latex](5 + \frac{S}{2})(S) - S^2 = 12[/latex]

    Solve for two values of [latex]S[/latex]
    Put them back into your linear equation and get two values for [latex]r[/latex]


  • #3
    Mr Pseudonym
    Closed Accounts Posts: 1,237 ✭✭✭Mr Pseudonym


    Nimrod 7 wrote: »
    Substitute one into the other. More specifically, substitute the linear equation into curve/circle.

    [latex]
    2r = 10 + S[/latex]

    [latex]r = 5 + \frac{S}{2}
    [/latex]


    [latex](5 + \frac{S}{2})(S) - S^2 = 12[/latex]

    Solve for two values of [latex]S[/latex]
    Put them back into your linear equation and get two values for [latex]r[/latex]

    Very fancy - Nimrod went all Latex on your ass! Ofc, you could also have substituted [latex]{S} = 2r - 10[/latex]

    You can compare your answers with this.


  • #4
    PKdude
    Registered Users Posts: 101 ✭✭PKdude


    I got it now. Thanks very much guys, I would have been stuck on that one for ages before giving up! Thanks again!


  • #5
    Peregrine
    Moderators, Education Moderators Posts: 26,403 Mod ✭✭✭✭Peregrine


    Mr Pseudonym wrote: »
    Very fancy - Nimrod went all Latex on your ass! Ofc, you could also have substituted [latex]{S} = 2r - 10[/latex]
    :pac:

    True, it makes no odds which one you substitute.

    If you substitute [latex]r[/latex], you'd have to square it. And if you substitute [latex]S[/latex], you'd have a fraction so you'd have to mutiply the whole line by 2.


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