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January 28, 2015

January 28, 2015

Posted by **Natasha** on Sunday, May 12, 2013 at 4:25am.

- Maths -
**Reiny**, Sunday, May 12, 2013 at 6:51am(1+2x)^n = 1 + n(2x) + n(n-1)/2! (2x) + n(n-1)(n-2)/3! (2x)^3 + ....

so (1-x)(1+2x)^2

= (1-x)(1 + n(2x) + n(n-1)/2! (2x)^2 + n(n-1)(n-2)/3! (2x)^3 + ....)

= 1 + 2nx + 4n(n-1)/2 x^2 + 8n(n-1)(n-2)/6 x^3 + ... - x - 2nx^2 - 4n(n-1)/2 x^3 - ..

so the only two terms with a first degree x term are

2nx - x

the 2nx - x = 19

2n - 1 = 19

2n = 20

n = 10

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