Question

Solve the simultaneous equations

5x + y = 21
x – 3y = 9

x = ________
y = ________

Answers

  1. Answer:

    5x+y=21……equation 1

    x-3y=9……equation 2

    from1:y=21-5x…..equation 3

    substitute y by 21-5x in equation 2

    x-3(21-5x)=9

    x-63+15x=9

    x+15x=9+63

    16x=72(we divide both sides by 16)

    16÷16=72÷16

    therefore x=9/2 or x=4,5

    substitute x by 4,5 or 9/2 in equation 3

    y=21-5(9/2) or y=21-5(4,5)

    y=-3/2 or y=-3/2

    prove

    5(9/2)-3/2=21

    -3/2-3(9/2)=9

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