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Mathematics 8 Online
OpenStudy (anonymous):

can any one solve this

OpenStudy (jhannybean):

So you have to solve for x?...

OpenStudy (zzr0ck3r):

-2 is one solution

OpenStudy (anonymous):

only we have to find x values

OpenStudy (zzr0ck3r):

so do you know how to do long division with polynomials?

OpenStudy (jhannybean):

Ohhh okay.

OpenStudy (anonymous):

i know i will solve it ...

OpenStudy (zzr0ck3r):

(2x^3-5x^2-14x+8)/(x+2)

OpenStudy (jhannybean):

How did you get the x+2..

OpenStudy (zzr0ck3r):

-2 is a solution

OpenStudy (zzr0ck3r):

so in factored form we know (x+2) is a factor

OpenStudy (jhannybean):

Would you explain HOW you got -2 as a solution? :P

OpenStudy (zzr0ck3r):

divide the whole thing by that to find other factors

OpenStudy (zzr0ck3r):

I guessed

OpenStudy (jhannybean):

lol -_-

OpenStudy (anonymous):

one is 4 and other one is 1/2 is it right friends

OpenStudy (zzr0ck3r):

there is an algorithm to solve these, google it.

OpenStudy (zzr0ck3r):

correct @msingh

OpenStudy (anonymous):

@zzr0ck3r thank u and also thank u @Jhannybean

OpenStudy (jhannybean):

np

OpenStudy (whpalmer4):

You can make some intelligent guesses about the roots of a polynomial if you know its coefficients. There's still some trial and error involved, but not so bad as just picking numbers out of the air. First, remember that any polynomial with roots \((r_1, r_2, ... r_n\)) can be written \[P(x) = (x-r_1)(x-r_2)...(x-r_n)\]Now think about what happens when you multiply two binomials: \[(ax+b)(cx+d) = acx^2 + adx + bcx + bd = acx^2 + (ad+bc)x + bd\]Notice that the final term depends only on the roots of the polynomial! Doesn't matter how many of those root binomials you multiply together, the final term always is just a product of the roots. So, if you factor the last term, you've got a good starting point for trial roots.

OpenStudy (jhannybean):

Actually,... this is a difference in cubes i believe. \[2x ^{3}-5x^2-14x+8= \color{#ff6600}{(2x^3-5x^2)}-\color{#ff0000}{(14x+8)}=\color{#664488}{(x-4) (x+2) (2 x-1)=0}\]And from this you can solve for your x-values. It's better than guess and check.

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