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Reply 20
Avatar for raheem94
raheem94
13
Original post by steve2005
Are you asking for help or just messing about.

The question you posted is incomplete, please give the full question as printed in the book.


See my post, i have attached the image.
Reply 21
Avatar for otrivine
otrivine
OP
14
Original post by raheem94
See my post, i have attached the image.


please help me raheem sorry i am just really stressing out come on we are friends help me pleasse
Reply 22
Avatar for raheem94
raheem94
13
Original post by otrivine
please help me raheem sorry i am just really stressing out come on we are friends help me pleasse


See post#19.
Reply 23
Avatar for otrivine
otrivine
OP
14
Original post by raheem94
For doing the question, just expand (1+x2)n \displaystyle \left( 1 + \frac{x}{2} \right)^n

Equate the coefficient of x2 x^2 in the expansion with 7.


so u mean substitue?
Original post by otrivine
so u mean substitue?


This is easy.
Screen shot 2012-05-23 at 21.08.07.png10.5KB
Reply 25
Avatar for otrivine
otrivine
OP
14
Original post by steve2005
This is easy.

oh so when you expand the brackets and get to x squared like 25xsquared = 7? you solve correct
Reply 26
Avatar for raheem94
raheem94
13
Original post by otrivine
so u mean substitue?


No.

(1+x2)n=…+n(n−1)2!(x2)2+…=…+n(n−1)2!(14x2)+… \displaystyle \left( 1 + \frac{x}{2} \right)^n = \ldots + \frac{n(n-1)}{2!}\left( \frac{x}2 \right)^2 + \ldots = \ldots + \frac{n(n-1)}{2!}\left( \frac14 x^2 \right) + \ldots

The coefficient of x2 x^2 is n(n−1)2!×14 \displaystyle \frac{n(n-1)}{2!} \times \frac14

It equals 7.

Hence solve, n(n−1)2!×14=7 \displaystyle \frac{n(n-1)}{2!} \times \frac14 = 7
Reply 27
Avatar for otrivine
otrivine
OP
14
Original post by raheem94
No.

(1+x2)n=…+n(n−1)2!(x2)2+…=…+n(n−1)2!(14x2)+… \displaystyle \left( 1 + \frac{x}{2} \right)^n = \ldots + \frac{n(n-1)}{2!}\left( \frac{x}2 \right)^2 + \ldots = \ldots + \frac{n(n-1)}{2!}\left( \frac14 x^2 \right) + \ldots

The coefficient of x2 x^2 is n(n−1)2!×14 \displaystyle \frac{n(n-1)}{2!} \times \frac14

It equals 7.

Hence solve, n(n−1)2!×14=7 \displaystyle \frac{n(n-1)}{2!} \times \frac14 = 7


1/4 x squared how ?
Reply 28
Avatar for raheem94
raheem94
13
Original post by otrivine
1/4 x squared how ?


(x2)2=x24=14x2 \displaystyle \left( \frac{x}2 \right)^2 = \frac{x^2}{4} = \frac14 x^2

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