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28 March, 12:41

Solve the system

-4x+8y=20

2x+2y=-30

+1
Answers (2)
  1. 28 March, 13:48
    0
    x = - 13 and y = - 4

    Step-by-step explanation:

    -4x + 8y = 20 ... eqn 1

    2x + 2y = - 30 ... eqn 2

    Step 1: Multiply eqn 1 by 2 and eqn 2 by 4

    (-4x + 8y = 20) * 2

    (2x + 2y = - 30) * 4

    we will have

    -8x + 16y = 40 ... eqn 3

    8x + 4y = - 120 ... eqn 4

    Step 2: Add eqn 3 and 4 together

    20y = - 80

    Step 3: divide all through by 20

    y = - 80/20

    y = - 4

    Step 4: Substitute - 4 for y in eqn 1

    -4x + 8 (-4) = 20

    -4x - 32 = 20

    -4x = 20 + 32

    -4x = 52

    Step 5: Divide both sides by - 4

    x = 52/-4

    x = - 13
  2. 28 March, 14:40
    0
    {x, y} = {-35/3,-10/3}

    Step-by-step explanation:

    -4x+8y=20; 2x+2-30

    System of Linear Equations entered:

    [1] - 4x + 8y = 20

    [2] 2x + 2y = - 30

    Solve by Substitution:

    / / Solve equation [2] for the variable y

    [2] 2y = - 2x - 30

    [2] y = - x - 15

    / / Plug this in for variable y in equation [1]

    [1] - 4x + 8• (-x - 15) = 20

    [1] - 12x = 140

    / / Solve equation [1] for the variable x

    [1] 12x = - 140

    [1] x = - 35/3

    / / By now we know this much:

    x = - 35/3

    y = - x-15

    / / Use the x value to solve for y

    y = - (-35/3) - 15 = - 10/3

    Solution:

    {x, y} = {-35/3,-10/3}
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