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Posted by on Monday, June 29, 2009 at 11:44pm.

solve by substitution
7x+6y=7
x=58-9y
What is the solution of the system?
(7,-5)
is this correct?

  • math - , Tuesday, June 30, 2009 at 9:48am

    You can check your work by using the values you found for x and y in the equations to see if they match.

    7(7) + 6(-5) = 7
    49 - 30 = 7
    19 = 7

    7 = 58 - 9*(-5)
    7 = 58-45
    7 = 13

    Clearly, something is wrong.

    Substitute 58-9y for x in 7x+6y=7 (because x = 58-9y)

    7(58-9y) + 6y = 7
    406 - 63y + 6y = 7
    399 - 57y = 0
    399 = 57y
    y = 7

    x = 58 - 9y
    x = 58 - 9*7
    x = 58 - 63
    x = -5

    The answer is (-5,7). Always (x,y).

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