Friday 20 February 2015

`f(x)=e^(4x) , n=4` Find the n'th Maclaurin polynomial for the function.

Maclaurin series is a special case of Taylor series that is centered at a=0. The expansion of the function about 0 follows the formula:


`f(x)=sum_(n=0)^oo (f^n(0))/(n!) x^n`


 or


`f(x)= f(0)+(f'(0)x)/(1!)+(f^2(0))/(2!)x^2+(f^3(0))/(3!)x^3+(f^4(0))/(4!)x^4 +...`


To determine the `4th` Maclaurin polynomial from the given function `f(x)=e^(4x)` ,


we may apply derivative formula for exponential function:` d/(dx) e^u = e^u * (du)/(dx)`


Let `u =4x` then `(du)/(dx)= 4 `


Applying the values on the derivative formula for exponential function, we get:


...

Maclaurin series is a special case of Taylor series that is centered at a=0. The expansion of the function about 0 follows the formula:


`f(x)=sum_(n=0)^oo (f^n(0))/(n!) x^n`


 or


`f(x)= f(0)+(f'(0)x)/(1!)+(f^2(0))/(2!)x^2+(f^3(0))/(3!)x^3+(f^4(0))/(4!)x^4 +...`


To determine the `4th` Maclaurin polynomial from the given function `f(x)=e^(4x)` ,


we may apply derivative formula for exponential function:` d/(dx) e^u = e^u * (du)/(dx)`


Let `u =4x` then `(du)/(dx)= 4 `


Applying the values on the derivative formula for exponential function, we get:


 `d/(dx) e^(4x) = e^(4x) *4`


Applying `d/(dx) e^(4x)= 4e^(4x)`  for each `f^n(x)` , we get:


`f'(x) = d/(dx) e^(4x)`


          `=e^(4x) * 4`


         `= 4e^(4x)`


`f^2(x) = 4 *d/(dx) e^(4x)`


           `= 4*4e^(4x)`


           `=16e^(4x)`


`f^3(x) = 16*d/(dx) e^(4x)`


          `= 16*4e^(4x)`


          `=64e^(4x)`


`f^4(x) = 64*d/(dx) e^(4x)`


      `= 64*4e^(4x)`


      `=256e^(4x)`


Plug-in `x=0` , we get:


`f(0) =e^(4*0) =1`


`f'(0) =4e^(4*0)=4`


`f^2(0) =16e^(4*0)=16`


`f^3(0) =64e^(4*0)=64`


`f^4(0) =2564e^(4*0)=256`


Note: `e^(4*0)=e^0 =1` .


Plug-in the values on the formula for Maclaurin series. 


`f(x)=sum_(n=0)^4 (f^n(0))/(n!) x^n`


         `= 1+4/(1!)x+16x^2+64x^3+256/(4!)x^4`


        `=1+ 4/1x +16/(1*2)x^2 + 64/(1*2*3)x^3 +256/(1*2*3*4)x^4`


        `=1+ 4/1x +16/2x^2 + 64/6x^3 +256/24x^4`


        `= 1+4x+ 8x^2 + 32/3x^3 + 32/3x^4`


The 4th Maclaurin polynomial for the given function `f(x)= e^(4x)` will be:


`e^(4x) =1+4x+ 8x^2 + 32/3x^3 + 32/3x^4`


or `P_4(x) =1+4x+ 8x^2 + 32/3x^3 + 32/3x^4`

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