- #1

Mdhiggenz

- 327

- 1

## Homework Statement

Locate all relative maxima, relative minima ,and saddle points if any.

f(x,y)=ysinx

fx(x,y)=ycosx

fy(x,y)=sinx

ycosx=0 sinx=0

y=0 x=0,∏,2∏... up until infinity

Critical points at (0,0),(∏,0),(2∏,0)...

fxx(x,y)=-ysinx

fyy(x,y)= cosx

fxx*fyy-f(x,y)

^{2}→0-0=0 ∴ no relative extrema,

however the book says that fxx*fyy-f(x,y)

^{2}=-1 which means saddle point.

I don't understand if y is = to zero.. the function ysinx will always be zero..