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SAT Math 9.4 Algebra and Functions 1314 Views
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Description:
SAT Math 9.4 Algebra and Functions
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.
Full Transcript
- 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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