`f(x)=xsinx` Find the Maclaurin series for the function.

Expert Answers

An illustration of the letter 'A' in a speech bubbles

Maclaurin series  is a special case of Taylor series which is centered at a=0. We follow the formula:

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

or

`f(x) = f(0) + (f'(0))/(1!)x+(f''(0))/(2!)x^2+(f'''(0))/(3!)x^3 +(f^4(0))/(4!)x^4 +(f^5(0))/(5!)x^5 +...`

To list of `f^n(x)` up to `n=10` , we may apply the Product rule for differentiation: `d/(dx) (u*v) = u'*v +u*v` '.

`f(x) = xsin(x)`

`f'(x) = xcos(x)+sin(x)`

`f''(x) = 2cos(x)-xsin(x)`

`f'''(x) =- xcos(x)-3sin(x)`

`f^4(x) = xsin(x)-4cos(x)`

`f^5(x) = xcos(x)+5sin(x)`

`f^6(x) = 6cos(x)-xsin(x)`

`f^7(x) = -xcos(x)-7sin(x)`

`f^8(x) = xsin(x)-8cos(x)`

`f^9(x) = xcos(x)+9sin(x)`

`f^(10)(x)= 10*cos(x)-x*sin(x)`

Note: `d/(dx)x=1` ,  `d/(dx) cos(x) =-sin(x)` , and `d/(dx) sin(x)=cos(x)` .

Plug-in x =0, we get:

`f(0) = 0*sin(0)`

         `=0*0`

         `=0`

`f'(0) = 0*cos(0)+sin(0)`

         `=0*1+0`

         `=0`

`f''(0) = 2cos(0)-0*sin(0)`

           `=2*1-0*0`

           `=2`

`f'''(0) =- 0*cos(0)-3sin(0)`

            `=-0*1-3*0`

            `=0`

`f^4(0) = 0*sin(0)-4cos(0)`

          `=0*0 -4*1`

          `=-4`

`f^5(0) = 0*cos(0)+5sin(0)`

          `=0*1+5*0`

          `=0`

`f^6(0) = 6cos(0)-0*sin(0)`

          `=6*1-0*0`

          `=6`

`f^7(0) = -0*0cos(0)-7sin(0)`

           `=-0*1-7*0`

           `=0`

`f^8(0) =0*sin(0)-8cos(0)`

          `=0*0-8*1`

          `=-8`

`f^9(0) = 0*cos(0)+9sin(0)`

           `=0*1+9*0`

           `=0`

`f^(10)(0)= 10*cos(0)-0*sin(0)`

            `=10*1-0*0`

            `=10`

Note: `cos(0)=1` and `sin(0) =0` .

Plug-in the values in the formula, we get:

`f(x) = 0 + 0/(1!)x+2/(2!)x^2+0/(3!)x^3+(-4)/(4!)x^4+0/(5!)x^5`

`+6/(6!)x^6+ 0/(7!)x^7+(-8)/(8!)x^8+0/(9!)x^9 +10/(10!)x^10+...`

 

`=0 + 0/(1)x+2/(1*2)x^2+0/(1*2*3)x^3-4/(1*2*3*4)x^4 `

`+ 0/(1*2*3*4*5)x^5 + 6/(1*2*3*4*5*6)x^6+0/(1*2*3*4*5*6*7)x^7`

` -8/(1*2*3*4*5*6*7*8)x^8 + 0/(1*2*3*4*5*6*7*8*9)x^9 + 10/(1*2*3*4*5*6*7*8*9*10)x^(10)+...`

 

`=0 + 0+2/2x^2+0/6x^3-4/24x^4 + 0/120x^5 + 6/720x^6 `

`+0/5040x^7 -8/40320x^8 + 0/362880x^9 +10/3628800x^(10)+...`

 

`=0 + 0+x^2+0-1/6x^4 + 0 + 1/120x^6`

`+0-1/5040x^8 + 0+1/362880x^(10)+...`

 

`=x^2 -1/6x^4 + 1/120x^6 -1/5040x^8 +1/362880x^(10)+...`

Therefore, the Maclaurin series for the function` f(x) =xsin(x)` can be expressed as:

`xsin(x)=x^2 -1/6x^4 + 1/120x^6 -1/5040x^8 +1/362880x^(10)+...`

See eNotes Ad-Free

Start your 48-hour free trial to get access to more than 30,000 additional guides and more than 350,000 Homework Help questions answered by our experts.

Get 48 Hours Free Access
Approved by eNotes Editorial Team