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Binomial expansion help?

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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Reply 1

mqb2766

Write out the expansion properly. You get a single quadratic equation, not two independent linear/quadratic equations.

(edited 3 years ago)

Reply 2

username3477548

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 :/

Reply 3

username3477548

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:/

Reply 4

mqb2766

Best way to learn about short cuts is to do it the long way first?

Reply 5

username3477548

Original post by mqb2766

Best way to learn about short cuts is to do it the long way first?

yeah lmao true

Reply 6

username3477548

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?