Math CentralQuandaries & Queries


Question from Anumba, a student:

4x + 2y = 4
7x - y = -11

Hi Anumba,

You didn't give any instructions but I expect you are to solve the pair of equations for $x$ and $y.$ I can help get you started.

Step 1.

Multiply both sides of the second equation by 2 and write down the first equation and the resulting second equation.

Step 2.

(The left side of equation 1 in step 1) plus (the left side of equation 2 in step 1) = (the right side of equation 1 in step 1) plus (the right side of equation 1 in step 1). Write this statement in mathematical form and simplify.

At this point you should see why I multiplied the original second equation by 2, the $y$ terms in step 2 cancel out and you have one equation is $x.$ Solve this equation for $x,$ substitute into one of the original equation and solve for $y.$ Make sure that you verify your answer.


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