Question #ec325

1 Answer
Jul 28, 2016

The perpendicular from origin O to a normal to y=loge(x) at point P is the segment OP.
It's length is X2P+Y2P, where XP is the abscissa of point P and YP=loge(XP).

Explanation:

Normal to a curve at point P lying on this curve, by definition, is a line perpendicular to a tangent to a curve at this point (presuming the curve is smooth and has a tangent, otherwise a normal is undefined).

Since OP is a tangent to curve y=loge(x) from origin O to point P lying on this curve, it is also a perpendicular to a normal to a curve at point P.

So, our task is to measure the length of OP.
This is done by Pythagorean Theorem as the distance between two points:
origin O with coordinates (0,0) and
point P on a curve with coordinates (XP,YP), where
YP=loge(XP).

OP=X2P+Y2P=X2P+log2e(XP)