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    • Thread Starter
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    Im having trouble doing this.
    It says leave answer in surd form
    2x+3y=13
    x^2+y^2=78

    i rearranged the first to equal

    x=(13-3y)/2

    then substitute it into the second

    ((13-3y)/2)^2+y^2=78

    then expand it all which i got
    13y^2-78y-143=0

    then i dont know what to do
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    Have you learnt the quadratic formula yet?
    That's what you have to use to solve the equation.
    • PS Helper
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    PS Helper
    Notice that 13 divides 13, 78 and 143, so divide through by 13; then use the quadratic formula.
 
 
 
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