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## Homework Statement

Find the 4 critical points f(x,y) = 5ycos(9x) closest to (0,0)

## Homework Equations

## The Attempt at a Solution

fx = -45ysin(9x)

fy = 5cos(9x)

fxx = -45*9ycos(9x)

fyy = 0

fxy = -45sin(9x)

y=0

x=pi/18

(0,pi/18) (0,pi/18 + pi/2) (0,pi/18 - pi/2) (0,pi/18 + 3pi/2) Was not correct.

(All 4 points need to be correct for me to check it )

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