Anonymous
Anonymous asked in Science & MathematicsMathematics · 9 years ago

help with this problem i'm stuck...?

Solve using the elimination method. Show your work. If the system has no solution or an infinite number of solutions, state this.

-3x+4y=1, -6x+6y=-3

So this is what i got--- multiply -2 to the first equation gives me -6x+8y=1..... then combine the 2 equation-6x+6y=-3 i get -12x+16y=-2 now what do i do..

Please show work.. thanks you imn advance........

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  • 9 years ago
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    You didn't have to muiltyply the 2nd line by 2...

    you have

    -6x + 8y=-2 [Muilty the whole thing by -2 even the anwser]

    -6x + 6y=-3 [Leave the 2nd eqation alone]

    2y=1 [Forget about the xs they now cancel each other out and subtract the rest of the eqation]

    y=2 [Divide 2]

    TO find the x you subsite the y and pick any of the 2 ORGINAL eqations

    3x + 4y =1

    3x + 8 =1 [Y=2 times that by the 4]

    3x =-7 [Subtract the 8]

    x=2.333333333333333333333333333 [Divide by 3]

    If you're not sure that you got it right you can plug in both anwsers to see if it's true

    -3x + 4y = 1

    -7 + 8 = 1 [Substute the x and y vaules and muiltiply I also rounded 6.999999 to 7]

    1 = 1 [The values match so I'm right]

  • 9 years ago

    multiply by -2 gives you +6x - 8y = -2. Combine and you get 6x - 6x +6y -8y = -2 -3 or -2y = -5 which means y = 5/2. Substitute his value into the first equation and you get -3x + 4*(5/2) = 1 or -3x + 10 = 1

    or -3x = -9 which means x = 3.

  • 9 years ago

    First mult first definition by -2

    6x - 8y = -2

    -6x+6y = -3

    then add or subtract

    0x - 2y = -5

    y = 2.5

    and then -3x + 4(2.5) = 1

    -3x + 10 = 1

    -3x = -9

    x = 3

    so answer would be (3, 2.5)

  • 9 years ago

    what you want to do is eliminate ONE of the variables.

    1. Multiply -2 to the first equation -> 6x-4y= -2

    2. Then line them up like this: 6x - 4y= -2

    -6x+ 6y= -3

    3. Add them up. 6x + -6x=0, -4y + 6y= 2y, -2 + -3 = -5

    4. the equation that you end up with is: 2y=-5

    5. Solve for y.

    6. Plug in the number you get for y in the first (or second) equation.

    7. Solve for x.

    Voila!

    I'm not going to do all of it for you, so you have to do the actual math...

    Source(s): Knowledge.
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  • Anonymous
    9 years ago

    Multiply the first equation by -2.

    -2(-3x+4y)=-2(1)

    6x-8y=-2

    Then add the two equations.

    6x -8y=-2

    -6x+6y=-3

    ---------------

    -2y =-5

    -2y=-5

    y=5/2

    Then plug in the value of y into either of the two original equations.

    -3x+4y=1

    -3x+4(5/2)=1

    -3x+10=1

    -3x=-9

    x=3

    Answer: x=3 and y=5/2

  • 9 years ago

    Multiplying the first eqn by -2 does not give you -6x + 8y = 1.... Please try again.

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