Question

why can't you use the second derivative test to determine if the function has max/min or a saddle point at the coordinates (x,y) if the coordinates are a part of the boundary points.?

Answer 1

is this calculus?

Answer 2

Yes it is :)

Answer 3

For example, if im looking at this function http://prntscr.com/28fgxf
and i find that \[f_x(x,y)=0 <=> y=0\]and
\[f_x(x,0)=0 <=> x=0\]
Then i've got a boundry point at (0,0)
why can't I / why shouldnt i use the second derivative test ?

Answer 4

Can't boundry points be stationary ?

Answer 5

*Typeo \[f_y(x,0)=0 <=> x=0\]

Answer 6

if f''(x) = 0, what can you say about the point?

Answer 7

I don't get what you wrote ? Do you mean \[f_{xx}(x,y)\]
the second partiel derivative of x ?

Answer 8

* in regard to x, or how you say it, english is not my main language, im sorry :)