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jimthompson5910 (jim_thompson5910):
y = x^3+x^2+4x+4
y = (1)^3+(1)^2+4(1)+4 ... plug in x = 1
y = 1 + 1 + 4(1) + 4
y = 1 + 1 + 4 + 4
y = 10
Since this is NOT zero, this means x = 1 is NOT a root or zero
jimthompson5910 (jim_thompson5910):
so it can't be C
OpenStudy (anonymous):
Oh, that's a simpler way to do it when you have the zeros given. Didn't see that :o
OpenStudy (anonymous):
i need help i dont get it
OpenStudy (anonymous):
The zeros are where the equation crosses on the x-axis on the graph.
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OpenStudy (anonymous):
The normal way (or the way I learnt it) is you have to factor your equation first so then you can find the zeros but @jim_thompson5910 's idea is way simpler.
jimthompson5910 (jim_thompson5910):
if x = 1 is a zero, then plugging it into some equation *should* give you y = 0
jimthompson5910 (jim_thompson5910):
ex:
if y = x-1
then x = 1 is a zero because
y = x-1
y = 1-1 .. plug in x = 1
y = 0
So this shows that x = 1 is a root or zero of y = x-1
OpenStudy (anonymous):
would it be b then
jimthompson5910 (jim_thompson5910):
what do you get when you plug x = 1 into y = x^3+x^2-4x-2
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OpenStudy (anonymous):
help
pleezzz
jimthompson5910 (jim_thompson5910):
y = x^3+x^2-4x-2
y = (1)^3+(1)^2-4(1)-2
y = ???
OpenStudy (anonymous):
y= -8
jimthompson5910 (jim_thompson5910):
that is NOT y = 0, so choice B is also out
jimthompson5910 (jim_thompson5910):
btw it should be y = -4, but that's still not 0
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OpenStudy (anonymous):
so what is the answer
jimthompson5910 (jim_thompson5910):
well you've eliminated B and C so far
jimthompson5910 (jim_thompson5910):
try out A
OpenStudy (anonymous):
ok
OpenStudy (anonymous):
is it a
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jimthompson5910 (jim_thompson5910):
what do you get when you plug in x = 1
OpenStudy (anonymous):
i got 3
jimthompson5910 (jim_thompson5910):
which is not 0, so x = 1 is not a root for choice A
OpenStudy (anonymous):
so its d
jimthompson5910 (jim_thompson5910):
yep
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