Question about polynomials

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Anonymous
Question about polynomials 2016-06-12 19:39:07 Post No. 139471
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Question about polynomials Anonymous 2016-06-12 19:39:07 Post No. 139471 [Report]

I ran into a question on the SAT that I had to skip due to time constraints, and I want to figure out how to do it correctly.

It was something like this:

f(x) = (x+1)(x-3)(x+5)(2-x) expanded is:
f(x) = -x^4-x^3+Ax^2-11x-30

What is the value of A?

So is there a shortcut for finding the coefficients of larger order polynomials given the roots? Obviously expanding the entire thing is not the correct way... right?

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Anonymous 2016-06-12 20:01:43 Post No.139482
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Anonymous 2016-06-12 20:01:43 Post No.139482 [Report]

>>139471
It is, however, you don't have to expand it entirely. It'd be suffice if you just Multiplied the first two and the last to sets of parenthesis.
You'd end up with : (x^2-2x-3)(-x^2-3x+10)
And since you only care about whatever's next to the x^2 in the final version of the equation,
You just have to to this: (-2x*10)+(-3x*-3)
There's no need for a shortcut you just have to get used to doing it quickly.

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Anonymous 2016-06-12 20:04:27 Post No.139483
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Anonymous 2016-06-12 20:04:27 Post No.139483 [Report]

>>139482
Fuck, I meant (x^2*10)+(-x^2*-3)

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Anonymous 2016-06-12 20:07:21 Post No.139484
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Anonymous 2016-06-12 20:07:21 Post No.139484 [Report]

>>139482
Oh shit now I understand. Thanks for the reply!

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Anonymous 2016-06-12 20:12:35 Post No.139486
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Anonymous 2016-06-12 20:12:35 Post No.139486 [Report]

Same exact format of question on the ACT, such a fun test.

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Anonymous 2016-06-12 20:17:43 Post No.139489
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Anonymous 2016-06-12 20:17:43 Post No.139489 [Report]

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