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31 January, 15:22

Can some one answer all of these questions

9) y = - 8x

2x + 4y = 0

10) 6x + 7y = 20

y = 2x

11) - 3x - 5y = 6

y = - 3

12) 6x - 5y = 22

y = - 8

13) y = 2x

3x + 3y = - 18

14) y = 8x

-5x - 5y = 0

15) y = - 3

-5x - 3y = 14

16) y = 3x

-3x - y = - 24

+3
Answers (1)
  1. 31 January, 15:51
    0
    For question number (9) since 2x + 4y = 0 and y = - 8x, simply substitute the second equation into the first.

    2x + 4y = 2x + 4 (-8x) = 2x - 32x = - 30x = 0

    so x = 0 and y = 0

    For question (10)

    6x + 7y = 20 and y = 2x (substitute 2x everywhere you see y in the first equation). So

    6x + 7 (2x) = 20

    6x + 14x = 20

    20x = 20

    x = 1

    (now substitute 1 for x in any of the equations)

    y = 2x = 2 (1) = 2

    So x = 1 and y = 2

    Question (11)

    -3 (x) - 5y = 6 and y = - 3 so

    -3 (x) - 5 (-3) = 6

    -3x + 15 = 6

    -3x + 15 - 6 = 0

    15 - 6 = 3x

    9 = 3x

    3x = 9

    x = 3

    Question (12)

    6x - 5y = 22 and y = - 8

    6x - 5 (-8) = 22

    6x + 40 = 22

    6x = 22 - 40

    6x = - 18

    x = - 18/6

    x = - 3

    Question (13)

    3x + 3y = - 18 and y = 2x

    3x + 3 (2x) = - 18

    3x + 6x = - 18

    9x = - 18

    x = - 18/9

    x = - 2

    Question (14)

    -5x - 5y = 0 and y = 8x so

    -5x - 5 (8x) = 0

    -5x - 40x = 0

    -45x = 0

    x = 0 and y=8 (0) = 0

    Question (15)

    -5x - 3y = 14 and y = - 3

    -5x - 3 (-3) = 14

    -5x + 9 = 14

    -5x + 9 - 14 = 0

    9 - 14 = 5x

    5x = 9 - 14

    5x = - 5

    x = - 5/5 = 5

    Question (16)

    -3x - y = - 24 and y = 3x so

    -3x - (3x) = - 24

    -3x - 3x = - 24

    -6x = - 24

    x = - 24/-6

    x = 4 and if x = 4 and y = 3x, then y = 3 (4) = 12

    check the calculations and make sure they are correct
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