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Solving Equations by Elimination help?

how to find the point of intersection for

4x-9y=4

6x+15y= -13

But find lcm multiple for x not y first, b/c I can't do it properly if i start off with x.

whenever i do it i get:

(1) x 6 --> 24x-54y=24

(2) x 4 ---> 24x+60y=-52

............. -) ----------------------

............... -114y/-114=76/-114

.............................y=38/-57

that is not correct, it should simplify to -1/2 like it does when you do it for y.

Update:

* sorry, i meant to say, that is not correct, it should simplify to -1/2 like it does for x when you find lcm for y (54&60)

Update 2:

* sorry, i meant to say, that is not correct, it should simplify to -2/3, like it does for y the other way around

3 Answers

Relevance
  • 9 years ago
    Favorite Answer

    4x-9y=4.......................MULTIPLY BY 6

    6x+15y= -13....................MULTIPLY BY 4

    24x - 54y = 24

    24x +60y =-52

    SUBTRACT

    - 114y = 76

    y = - 76/114 = -38/57 = - 2/3

    6x + 15*(-2/3) = -13

    6x - 10= -13

    6x = -3

    x = -1/2

    ANSWER x = -1/2 y = -2/3

  • Bea
    Lv 5
    9 years ago

    Your work is correct, but you didn't reduce y all the way.

    y = 38 / -57 Now divide by 19

    y = - 2/3

    x = -1/2

    x and y will usually not be the same value.

    4x - 9(-2/3) = 4

    4x + 18/3 = 4

    4x = 4 - 18/3

    4x = -6/3

    4x = -2

    x = -2/4 = -1/2

  • Anonymous
    9 years ago

    They have a closer one in common, 12.

    4x - 9y = 4 (multiply by 3)

    6x + 15y = -13 (multiply by -2)

    12x - 27y = 12

    -12x - 30y = 26

    -57y = 38

    y = (-38/57) =(-2/3)

    (They are both divisible by 19, that is how they reduced to -2/3, you were correct)

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