lovelycharm
elimination 4x - 7y = 3
x - 7y = -15
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mjr632
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Do you understand how to substitute?
lovelycharm
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yeh
mjr632
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Okay, firstly, you want one equation as either Y or X by itself.
mjr632
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If you do that part, i'll then explain the next step.
lovelycharm
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okay wat the next step
mjr632
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write the equation you've got for your isolated variable in here.
lovelycharm
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|dw:1360887641308:dw| is that right how i solve for y
Rachel98
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- 7y + - 7y is not zero and 4x + x is 5x
Rachel98
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You need a variable to cross out when you add down. Try multiplying one of the equations by a certain number so that one variable crosses out when you add down.
lovelycharm
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could u show me the step please @Rachel98
Rachel98
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Okay, here is an example problem I'll draw it.
Rachel98
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|dw:1360888023089:dw|
Rachel98
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Now see how none of the variables cross off? So I'm going to try multiplying the first equation by - 1 and see what happens.
Rachel98
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|dw:1360888146491:dw|
Rachel98
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Now see if you add straight down a variable crosses off when you add down. - y and y can also be put as - 1y and 1y. Look at the numbers - 1 + 1 = 0, so that crosses off.
Rachel98
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|dw:1360888346035:dw|
Rachel98
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Now all we have to do is divide both sides by - 1, so undo the multiplication
Rachel98
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|dw:1360888489391:dw|
Rachel98
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So we have our x value, now what about y? What we do is we plug in the x value (substitute 8 for x) in one of the original equations. In this case the bottom equation is easier to do this.
lovelycharm
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could u help me with my problem cuz i dont understand ur problem
Rachel98
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|dw:1360888601809:dw|
Rachel98
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See, in my problem how I multiplied one equation by - 1? Try doing that with either one of your equations and then add down.
Rachel98
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Remember, a negative * a negative is a positive.
Rachel98
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|dw:1360888933281:dw|
Rachel98
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Did you get it? Give it a try. I'll check your answer and if you make a mistake I'll work through it for you.