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swissgirl
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Reduce the polynomial and find its complex roots
\(f(x)=x^4+5x^39x^285x136\)
 2 years ago
 2 years ago
swissgirl Group Title
Reduce the polynomial and find its complex roots \(f(x)=x^4+5x^39x^285x136\)
 2 years ago
 2 years ago

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swissgirl Group TitleBest ResponseYou've already chosen the best response.0
lol didnt know u were on
 2 years ago

swissgirl Group TitleBest ResponseYou've already chosen the best response.0
not quite sure how to reduce it since u start dealing with decimals. It shld be quite simple though
 2 years ago

KingGeorge Group TitleBest ResponseYou've already chosen the best response.1
By reduce do you mean factor?
 2 years ago

swissgirl Group TitleBest ResponseYou've already chosen the best response.0
i am assuming so
 2 years ago

KingGeorge Group TitleBest ResponseYou've already chosen the best response.1
Well, I have a couple ideas, so let's see if I can do this by hand... \[f(x)=x^4+5x^39x^285x136\\ f(x)=x^417x^2+5x^3+8x^217(5x8)\\ f(x)=x^417x^2+x^2(5x+8)17(5x+8)\\ f(x)=x^417x^2+(x^217)(5x+8)\\ f(x)=x^2(x^217)+(x^217)(5x+8)\\ f(x)=(x^217)(x^2+5x+8) \]
 2 years ago

KingGeorge Group TitleBest ResponseYou've already chosen the best response.1
So you can use the quadratic formula on \(x^2+5x+8\) to find the complex roots, and just \[x^217=0\implies x=\pm\sqrt{17}\]For the real roots.
 2 years ago

swissgirl Group TitleBest ResponseYou've already chosen the best response.0
Let me just see if I can follow what u did
 2 years ago

KingGeorge Group TitleBest ResponseYou've already chosen the best response.1
Take your time. I'm honestly very surprised I was able to factor that almost entirely by hand. (I used wolfram to check correctness, and to find the gcd of 85, 136).
 2 years ago

swissgirl Group TitleBest ResponseYou've already chosen the best response.0
idk if its possible. Dont drive urself crazy buttt I cant decipher what is squred and what is tripled. Is it possible to make it larger
 2 years ago

swissgirl Group TitleBest ResponseYou've already chosen the best response.0
whoops cubed lol
 2 years ago

KingGeorge Group TitleBest ResponseYou've already chosen the best response.1
\[\Large f(x)=x^4+5x^39x^285x136\\ \Large f(x)=x^417x^2+5x^3+8x^217(5x8)\\ \Large f(x)=x^417x^2+x^2(5x+8)17(5x+8)\\ \Large f(x)=x^417x^2+(x^217)(5x+8)\\ \Large f(x)=x^2(x^217)+(x^217)(5x+8)\\ \Large f(x)=(x^217)(x^2+5x+8)\]
 2 years ago

swissgirl Group TitleBest ResponseYou've already chosen the best response.0
Thanks :)
 2 years ago

swissgirl Group TitleBest ResponseYou've already chosen the best response.0
OKKKK so like will this method always work?
 2 years ago

KingGeorge Group TitleBest ResponseYou've already chosen the best response.1
Not always. This is just factoring by grouping, and while potentially useful, it is often difficult to identify the correct time to use it, and what to group together. I just got lucky that I guessed the right things to group. For example, if I had \[\Large f(x)=x^4+5x^310x^285x136\]instead, I would not be able to group it as easily.
 2 years ago

swissgirl Group TitleBest ResponseYou've already chosen the best response.0
ohhhh i seee. I guesss I have to play around. Not as simple as I wish it wld be. Thanks KG:)))))))))))
 2 years ago

KingGeorge Group TitleBest ResponseYou've already chosen the best response.1
You're welcome. I will note however, that if they tell you to factor something, it's usually possible to do it by hand with a little cleverness.
 2 years ago

swissgirl Group TitleBest ResponseYou've already chosen the best response.0
Haha So I hope and pray that it will be so. lol Thanks KGGGG
 2 years ago
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