You are asked to derive expressions for the average rates of change of the functions $\sin x, \cos x,$ and $\tan x$
In each case, assume that the interval is $[x, x+h] .$ (The results are used in calculus in the study of derivatives.)
Let $g(x)=\cos x .$ Show that
$$
\frac{\Delta g}{\Delta x}=(\cos x)\left(\frac{\cos h-1}{h}\right)-(\sin x)\left(\frac{\sin h}{h}\right)
$$