Monday, May 27, 2019

f(x)=1/(2+x)^3 Use the binomial series to find the Maclaurin series for the function.

Recall a binomial series  follows: 
(1+x)^k=sum_(n=0)^oo _(k(k-1)(k-2)...(k-n+1))/(n!)x^n
or
(1+x)^k = 1 + kx + (k(k-1))/(2!) x^2 + (k(k-1)(k-2))/(3!)x^3 +(k(k-1)(k-2)(k-3))/(4!)x^4+ ...
To evaluate given function f(x) =1/(2+x)^3 , we may apply  2+x = 2(1+x/2) .
The function becomes:
f(x) =1/(2(1+x/2))^3
Apply Law of Exponents: (x*y)^n = x^n*y^n at the denominator side.
1/(2(1+x/2))^3=1/(2^3(1+x/2)^3)
                = 1/(8(1+x/2)^3)
Apply Law of Exponents: 1/x^n = x^(-n) .
f(x) = 1/8(1+x/2)^(-3)
Apply the binomial series on (1+x/2)^(-3) . By comparing "(1+x)^k " with "(1+x/2)^(-3) " the corresponding values are:
x=x/2 and k =-3
Then,
(1+x/2)^(-3) =sum_(n=0)^oo _((-3)(-3-1)(-3-2)...(-3-n+1))/(n!)(x/2)^n
=1 + (-3)x/2 + ((-3)(-3-1))/(2!) (x/2)^2 + ((-3)(-3-1)(-3-2))/(3!)(x/2)^3 +((-3)(-3-1)(-3-2)(-3-3))/(4!)(x/2)^4+...
=1 -(3x)/2 + ((-3)(-4))/(2!) (x^2/4) + ((-3)(-4)(-5))/(3!)(x^3/8) +((-3)(-4)(-5)(-6))/(4!)(x^4/16)- ...
=1 -(3x)/2 +12/(2!) (x^2/4) -60/(3!)(x^3/8) +360/(4!)(x^4/16)- ...
=1 -(3x)/2 +(3x^2)/2 -(5x^3)/4 +(15x^4)/16- ...
Applying (1+x/2)^(-3) =1 -(3x)/2 +(3x^2)/2 -(5x^3)/4 +(15x^4)/16- ..., we get:
1/8(1+x/2)^(-3)=1/8*[1 -(3x)/2 +(3x^2)/2 -(5x^3)/4 +(15x^4)/16-...]
                    =1/8-(3x)/16 +(3x^2)/16 -(5x^3)/32 +(15x^4)/128- ...
Therefore, the Maclaurin series  for  the function f(x) =1/(2+x)^3 can be expressed as:
1/(2+x)^3=1/8-(3x)/16 +(3x^2)/16 -(5x^3)/32 +(15x^4)/128- ...

No comments:

Post a Comment

Summarize the major research findings of "Toward an experimental ecology of human development."

Based on findings of prior research, the author, Bronfenbrenner proposes that methods for natural observation research have been applied in ...