Question

Which is the best first step and explanation for solving this system of equations?

Answer 1

Answer:

  see below

Step-by-step explanation:

Since 2x appears on the left side of both equations, that term can be eliminated by subtraction, which is what the first choice suggests.

The result will be ...

  3y = 7 -4y +5 . . . . . . . . . second equation subtracted from the first

  7y = 12 . . . . . . add 4y

  y = 12/7 . . . . . . divide by 7

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However, the fact that 2x is by itself on the left side of the second equation suggest that substitution may also be a good option. Perhaps an equally good first step is to use the expression in the second equation to substitute for 2x in the first:

  (4y -5) +3y = 7

Either way, the resulting equation is 2-step.

  7y = 12 . . . add 5

  y = 12/7 . . . divide by 7

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The other suggested "first steps" do nothing useful.