Learning immediately: https://edu.csdn.net/course/play/26262/326625?utm_source=blogtoedu
rate = delta / delta x
a point rate curve slope of the line tangent to rate
CIRCLE
n*b->2pi*r
secant line secant
Tangent line tangent
lim(deltax ->0)delta f(x)/delta x
f(x)=x^n
f (x) '= nx ^ n-1
