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How do you know what to multiply in elimination?

User Asons
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Answer:

See below

Explanation:

When nether of the variable will fall out when adding together. For example:

2x + 5y = 13

-2x + 7y = 17

When I add these equation together, the variable x will drop out because 2x - 2x = 0 and we would be left with other the y variable which we then can solve for. 12y = 30

Now another example where the neither the x or y falls out.

x + 5y = 12

2x + 3y= 9

When I add these together, neither variable falls out.

3x + 8y = 21

BUT, if I multiply x + 5y = 12 though by -2 I get

-2x -10y = -24

Now when I add the two equation together the x's will drop out.

-2x -10y = -24

2x + 3y = 9

-7y = --15

User Alexander Golys
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