Given `f(x)=sin(8x)` , find the linear approximation at x=0:
(2) `f'(x)=8cos(8x)` . This is the slope of the line tangent to f(x) at x.
(3) `f'(0)=8` This is the slope of the tangent line at x=0
(4) y-0=8(x-0) or y=8x is the line tangent to f(x) at (0,0); this is the linear approximation to f(x).