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Arieln7s96 2 years ago I need help knowing what the difference is : Select the best possible first step to solving the following system by first eliminating the y variable. 5x-3y=1 7x-4y=2 My options are to: Multiply the first equation by 3 and multiply the second equation by 4. Multiply the first equation by -3 and multiply the second equation by -4. Multiply the first equation by -7 and multiply the second equation by 5. None of the above. My instinct is to multiply the equations by either 3 and 4 or -3 and -4, but I don't know what the difference is in multiplying by a negative or a positive.

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1. Arieln7s96

@ChmE Please help!

2. lilg132

are you sure you wrote the options correctly?

3. lilg132

and the question?

4. Arieln7s96

positive

5. mathstudent55

In elimination, you want to add or subtract the equations to eliminate one variable, here it's y. Your instinct is correct, but you have to be careful which equation you multiply by what. You want 12y or -12 y. The first equation should be multiplied by 4 or -4 and the second by 3 or -3. Notice they give you 3 with the second eq and 4 with the first one. That will not help. 5 and -7 would help eliminate x not y.

6. lilg132

which is why i think the question or options are wrong

7. Arieln7s96

Right, and i would think it would be -3 and 4 so I'm going to go ahead and go with none of the above

8. lilg132

either the question should be eliminate x first or the option should have multiply first equation by 4 and second by 3 or multiply first equation by -4 and second by -3 or something like that

9. lilg132

oops i didnt even see none of the above so yes thats the answer

10. Arieln7s96

Thanks so much!

11. ChmE

definitely non of the above. You're correct

12. ChmE

It's tough to answer these questions without knowing if they want to eliminate by addition or subtraction. Subtraction the coefficients should have the same sign. Addition they should be opposite.

13. Arieln7s96

Thanks!

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