Math help

How would you solve these systems by elimination? I'm in desperate need of help!

1. -35x-15y=0
-56x+24y=0

2. -56x+72y=-16
-49x+63y=-14

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  1. we must find a common multiple of something here
    15 = 3*5
    24 = 3*8
    so I guess we could use 3*5*8 = 120

    15 * 8 = 120 so multiply first eqn by 8
    24 * 5 = 120 so multiply second by 5
    - 280 x - 120 y = 0
    - 200 x + 120 y = 0
    -------------------- add
    -480 x = 0
    so x = 0
    and y = 0
    which we could have said back at the beginning if we had sketched graphs

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    posted by Damon
  2. in the second one both 56 and 49 have common factor 7 which we will take advantage of
    56 = 7 * 8
    49 = 7*7 so use 7*7*8 = 392

    56 *7 = 392 so multiply first by 7
    49 *8 = 392 so multiply second times 8

    I think you can take it from there.

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    posted by Damon
  3. On the first one how did you get -280 and -200?

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  4. -280 = -35 * 8

    -280 =-56 * 5
    sorry, 280 not 200, does not matter, solution is origin (0,0) anyway
    both of those lines are through the origin having no b in y = m x + b

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    posted by Damon

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