HESI A2 Exam: System of Equations
•What is the first thing you are trying to do with systems of equations problems?
With systems of equations, you will be looking at two equations. You need to look to either combine the equations so that one of the variables is eliminated, or look to plug in one of the equations into the other. Let’s take a look at a few examples.
2x + y = 7
y = 5
For this problem, we can just plug in y =5 into the first equation, and solve for x.
2x + 5 = 7
2x = 2
x = 1
Here’s another one that is a bit harder.
Solve for x:
2x + y = 7
x + y = 5
For something like this, we need to make one of the equations have a –y (negative y) so that when we combine the equations the y’s are eliminated and then we can solve for x. So we will multiply the bottom equation by -1 on both sides. Now here is what the two equations look like.
2x + y = 7
-x - y = -5
Now we combine the two equations (add them together)
x = 2 (We are done. That’s our answer).
If they asked us to also solve for y, then we can go back and plug in 2 for x and solve. It does not matter which equation you plug in. In both cases you will get y = 3.
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