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Math III Videos 103 videos

Unit Rate
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Approximately 874 people per day wonder what a unit rate is. If you're one of them, check out our video on unit rates and how to use them. (We just...

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SAT Math 9.4 Algebra and Functions 1300 Views


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Description:

SAT Math 9.4 Algebra and Functions

Language:
English Language

Transcript

00:02

Hope you left room for an extra helping of Shmoop.

00:05

If 3x squared + 5x = 12 and x is not an integer, then what must x be?

00:14

All right, so this question looks simple enough.

00:16

We have to find the solution to this equation where x ISN’T an integer.

00:20

So, first we can move 12 to the left side to get 3x squared + 5x – 12 = 0.

00:26

This format look familiar to ya?

00:28

Well, it really doesn’t look like we can factor this one, so let’s apply the quadratic formula.

00:35

So with 3 as a, 5 as b and negative 12, guest starring as c…we can now apply our formula.

00:42

Negative 5 plus or minus radical 25 plus negative 4 times 3 times negative 12…equals 144 all over 6.

00:50

…and 144 plus 25 is 169…ooh, magic number…

00:55

…so we have negative 5 plus or minus 13…all over 6.

01:00

Now we can just separate out the two plus or minus options…

01:04

…and we have negative 5 plus 13 over 6 and negative 5 minus 13 over 6.

01:11

The first one simplifies to 8 over 6, or just 4/3…

01:15

…and the second one simplifies to negative 18 over 6, or just negative 3.

01:19

So, since the question asks us for the non-integer solution to the equation,

01:24

we can forget about that last one.

01:26

Later, negative 3. So yeah…the answer is 4/3.

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