Abraham Lincoln, i've read that story a long time ago myself and I remember who said that.
Given:
Planes X and Y are perpendicular to each other
Points A, E, F, and G are points only in plane X
Points R and S are points in both planes X and Y
Lines EA and FG are parallel
The lines which could be perpendicular to RS are EA and FG.
You have to use implicit derivative
dy / dx = y'
xy^3+y=3x
y^3 + 3xy^2 y' + y' = 3
[3xy^2 + 1) y'= 3 - y^3
3 - y^3
y' = ----------------- <-----------answer
3xy^2 + 1
Thanks merry Christmas to you
