Sagot :
Answer:
prin·ci·pal ax·is
/ˈprinsəpəl ˈaksəs/
nounPHYSICS
each of three mutually perpendicular axes in a body about which the moment of inertia is at a maximum.
Answer:
a line that passes through the center of curvature of a lens so that light is neither reflected nor refracted; "in a normal eye the optic axis is the direction in which objects are seen most distinctly"