c2 help

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#1
how would i work out b)
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#2
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2 years ago
#3
What did you get for part a? Once you have part a you compare coefficients. They tell you the coefficient of x^2 is 525.
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2 years ago
#4
So in the first part you found the first four terms. The third term should be "..."x^2. The coefficient of this is equal to 525. Then rearrange to find the value of a since that is the only variable in this case
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#5
so i got for a)

1+7ax +21a^2x^2 + 35a^3x^3

since they gave me the coeff of x^2 do i focus on only the x^2 terms?
not sure what to do from here
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2 years ago
#6
(Original post by mathshelppp)
so i got for a)

1+7ax +21a^2x^2 + 35a^3x^3

since they gave me the coeff of x^2 do i focus on only the x^2 terms?
not sure what to do from here
Yup, so you make the 21a^2=525. Then solve for a. You will get two solutions
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#7
(Original post by -Phoenix-)
Yup, so you make the 21a^2=525. Then solve for a. You will get two solutions
oh loool i just saw i wrote that on my paper yesterday
thanks

i got +/- 5
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2 years ago
#8
(Original post by mathshelppp)
oh loool i just saw i wrote that on my paper yesterday
thanks

i got +/- 5
No worries
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#9
also
theres two forumlas
and i know when to use each
the ncr when its for positive integers and the other for all terms

shall i just use the one for all?

-Phoenix-
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2 years ago
#10
(Original post by mathshelppp)
also
theres two forumlas
and i know when to use each
the ncr when its for positive integers and the other for all terms

shall i just use the one for all?

-Phoenix-
May I know which two you are talking about? I only know of one
I think that one of them may have been derived from the other
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#11
(Original post by -Phoenix-)
May I know which two you are talking about? I only know of one
I think that one of them may have been derived from the other
http://www.examsolutions.net/tutoria...=C2&topic=1308

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2 years ago
#12
Yeah, I see what you mean. The first formula with the (1 + b)^n, will only work when there is a one, and no other number. If you get a number inside the brackets, then I would say to take it out and then use the formula with (1 + b)^n. I think it would be safer, but you can learn both if you have extra time in the exam and want to check the answers. However, I've never seen a question with (a + b)^n in a C2 paper before.
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#13
(Original post by -Phoenix-)
Yeah, I see what you mean. The first formula with the (1 + b)^n, will only work when there is a one, and no other number. If you get a number inside the brackets, then I would say to take it out and then use the formula with (1 + b)^n. I think it would be safer, but you can learn both if you have extra time in the exam and want to check the answers. However, I've never seen a question with (a + b)^n in a C2 paper before.
the ncr one i think is better

oh there is!
http://pmt.physicsandmathstutor.com/...0expansion.pdf
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2 years ago
#14
(Original post by mathshelppp)
the ncr one i think is better

oh there is!
http://pmt.physicsandmathstutor.com/...0expansion.pdf
The ncr method is good as well. To be honest, it doesn't really matter which one you use as long as you get the right answer. However, in C3/C4, I have been taught the method to take out a factor before using factor formula. I didn't know that another way existed
Can't believe I didn't revise that last year
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#15
(Original post by -Phoenix-)
The ncr method is good as well. To be honest, it doesn't really matter which one you use as long as you get the right answer. However, in C3/C4, I have been taught the method to take out a factor before using factor formula. I didn't know that another way existed
Can't believe I didn't revise that last year
no thats right!! the taking the factor out i use for c4
loool yeah im going to learn both anyway
thank you xx
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#16
(Original post by -Phoenix-)
The ncr method is good as well. To be honest, it doesn't really matter which one you use as long as you get the right answer. However, in C3/C4, I have been taught the method to take out a factor before using factor formula. I didn't know that another way existed
Can't believe I didn't revise that last year

i can do questions like b but this is weird, i think they meant the coeff of x^3 is double the coeff of x^2
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2 years ago
#17
(Original post by mathshelppp)

i can do questions like b but this is weird, i think they meant the coeff of x^3 is double the coeff of x^2
Yes, you are most probably correct. Check the mark scheme afterwards to make sure though
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