Home page for accesible maths Math 101 Chapter 4: Taylor series and complex numbers

Style control - access keys in brackets

Font (2 3) - + Letter spacing (4 5) - + Word spacing (6 7) - + Line spacing (8 9) - +

4.8 The Maclaurin series for sine

Example

The Maclaurin series of sin⁡x\sin x\,.

Solution. We calculate the successive derivatives in left-hand column and their values at x=0x=0\, in the right-hand columns:

f⁢(x)=sin⁡x,      f⁢(0)=0;f(x)=\sin x,\qquad\qquad\qquad f(0)=0;\qquad\qquad
f′⁢(x)=cos⁡x      f′⁢(0)=1;f^{\prime}(x)=\cos x\qquad\qquad\qquad f^{\prime}(0)=1;\qquad\qquad
f′′⁢(x)=-sin⁡x   f′′⁢(0)=0;f^{\prime\prime}(x)=-\sin x\quad\qquad\qquad f^{\prime\prime}(0)=0;\qquad\qquad
f′′′⁢(x)=-cos⁡x   f′′′⁢(0)=-1;f^{\prime\prime\prime}(x)=-\cos x\quad\qquad\qquad f^{\prime\prime\prime}(0)=-% 1;\qquad\qquad
f(4)⁢(x)=sin⁡x      f(4)⁢(0)=0;f^{(4)}(x)=\sin x\qquad\qquad\qquad f^{(4)}(0)=0;\qquad\qquad

and the pattern repeats with a period of four; hence only odd powers appear and the signs alternate. We feed the right-hand coefficients into the general Maclaurin formula to get