Wednesday

October 22, 2014

October 22, 2014

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

**Answer this Question**

**Related Questions**

maths - find the first 3 terms in the expansion of (x+4)(1+3x)^-2 as a series in...

Maths - The 3rd term of an AP is 10 more than the first term while the fifth ...

maths - Obtain the binomial expansion of (2-x) (1+1/2x)^8 in ascending powers of...

maths - in the binomial expansion of (1+x/k)^n, where k is a constant and n is a...

maths - given that x+1/x=3 (a) expand (x+1/x)^3 and use your expansion to show ...

maths - Given that the first term of an A.P is 7 and its 10th term is twice its ...

Algebra - Find the product (1 - 3x) (x^2 - 6x - 4)x^2 A. -3x^5 + 19x^4 + 6x^3 - ...

maths-binomial theorem--plse help - find the greatest term in the expansion of (...

maths - There are 6 terms in an A.P. 6th term is 3 times the second term and 4th...

Maths - Find 8 terms of the arithmetic progression if the second term is 2 and ...