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For the equation y = -2x - 1, when you substitute x = 4 into the equation, what is the result? A. -8 B. -9 C. 9 D. 8

User Waruna K
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4 votes

Answer:

y = -9

Explanation:

These are simple. When it says to "substitute" x = 4, it's literally saying to put 4 where x is.

Because remember: x is a variable, it can be anything. But whatever it is, y is -2 times it, and then minus 1. So they're really asking, "If x was a 4, like literally if I put a 4 in that variable's place, what would y come out to be?"

Reread that if you need to, but understand it and it'll make your future life so much simpler.

So let's do that. Write the equation first:

y = -2x -1

Now put a 4 where the x is. "Substitute x = 4 into the equation." I like to say "plug in" 4 for x. However you need to think about it, you now KNOW that x is 4, so just put a 4 in that place:

y = -2(x) -1

y = -2(4) -1

Do you see that? I just put 4 "in" for x. Where x had been, I put a 4. Now solve it ("solve for y" is what they call it):

y = -8 - 1

y = -9

Not too, too hard, right? And by the way, what you just did was calculate a set of (x,y) coordinates in case you were asked to plot this equation. "When x = 4, then y = -9." That's a point you can plot at (4,-9).

Keep plugging away at this stuff!

User Sategroup
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