Why is cos(pi) and cos (-pi) both equal to -1?
February 20th, 2023
A full circle is ##2pi##
##pi## is half way around the circle counter-clockwise.
##-pi## is half way around the circle clockwise.
##cos(pi) = cos(-pi)## are the both ##cos## values for the same place
They are both equal to ##(-1)##
because
if viewed as a unit circle centered on the Cartesian origin
the ##cos## is the ##x## value
and, at halfway around the unit circle,
##x=-1##
