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00:02

And we're getting math-y with it...

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x + y = 1

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y + z = -4

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x + z = -19

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Using the above equations, what is the value of z?

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And here are the potential answers...

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What we've got here is a system of 3 equations, and 3 variables to solve for.

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The first equation is x + y = 1.

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We can subtract x from both sides to get y = 1 - x.

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Now, let's plug in what we know into the second equation, y + z = -4.

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For example, we can subtract y from both sides to get z = -4 - y.

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What do we do next?

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Or, we can substitute y out of this equation.

00:48

Now we need to define x in terms of z.

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Our last equation can help with that.

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So, let's subtract z from both sides,

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and we will see that x is equal to -19 - z.

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Now we can just substitute x out of our previous equation.

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First, we'll distribute the negative sign into the parentheses.

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Then, we'll do it again for the second pair of parentheses.

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Finally, we'll add z to both sides, and combine the constants.

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After this, we'll divide both sides by 2, and find that z = -12.

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So our answer is (A).

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