# Binomial expansion help?

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Thread starter 5 months ago
#1
With question 7, i cant get to the correct answer?
I thought there are two ways of getting x^2, one by just having an x^2 term from the right bracket and multiplying that by 5, and the other is by having a x term and then multiplying that by x.
Either way is not getting me to the correct answer. ive attached my shity working incase ur interested lol.
Also by finding x^2 the first way i mentioned, that gives an k^2, so therefore that itself gives two vlaues of k. So altogether i get like 3 values which is DEFO wrong....

thank you!!
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5 months ago
#2
Write out the expansion properly. You get a single quadratic equation, not two independent linear/quadratic equations.
Last edited by mqb2766; 5 months ago
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Thread starter 5 months ago
#3
(Original post by mqb2766)
Write out the expansion properly. You get a single quadratic equation, not two independent linear equations.
ooh so i have to expand it completely??
i was tryna take a short cut lol guess that didn't work out :/
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Thread starter 5 months ago
#4
(Original post by mqb2766)
Write out the expansion properly. You get a single quadratic equation, not two independent linear/quadratic equations.
got it lol thanks for ur help!

i was sort of close with my initial method i just forgot to add them together which is so annoying:/
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5 months ago
#5
Best way to learn about short cuts is to do it the long way first?
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Thread starter 5 months ago
#6
(Original post by mqb2766)
Best way to learn about short cuts is to do it the long way first?
yeah lmao true
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Thread starter 5 months ago
#7
(Original post by mqb2766)
Write out the expansion properly. You get a single quadratic equation, not two independent linear/quadratic equations.
could I ask you a quick question abt nCr?

If we are given nC2 is 15 is there a way to work out the value of n without trial and error using a calc? using the formula would be really complicated cuz of the factorials right?
Last edited by Qxi.xli; 5 months ago
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5 months ago
#8
Why is the formula difficult? As it's choose 2, it will give an easy quadratic in n.
Again, do it the long way, and learn the shortcut.
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Thread starter 5 months ago
#9
(Original post by mqb2766)
Why is the formula difficult? As it's choose 2, it will give an easy quadratic in n.
Again, do it the long way, and learn the shortcut.
Ignore
Last edited by Qxi.xli; 5 months ago
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Thread starter 5 months ago
#10
(Original post by vix.xvi)
.
nvvmmm lol i got it thanks!! ignore that
Last edited by Qxi.xli; 5 months ago
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