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Answer:
[tex]y =-x[/tex] ---- critical point
local minima
Step-by-step explanation:
Given
[tex]f(x,y) = x^2 + y^2 + 2xy[/tex]
Required
Determine the critical point
Differentiate w.r.t x
[tex]f_x =2x + 2y[/tex]
Differentiate w.r.t y
[tex]f_y =2y + 2x[/tex]
Equate both to 0
[tex]2x + 2y =0[/tex]
[tex]2y =0-2x[/tex]
[tex]2y =-2x[/tex]
Divide by 2
[tex]y =-x[/tex] ----- in both equations
Hence:
The critical point is: [tex]y =-x[/tex]
Solving (b):
We have:
[tex]f_x =2x + 2y[/tex]
[tex]f_y =2y + 2x[/tex]
This is represented as:
[tex]D = \left[\begin{array}{cc}2&2\\2&2\end{array}\right][/tex]
Calculate the determinant
[tex]|D| =2 * 2 -2 * 2[/tex]
[tex]|D| = 4-4[/tex]
[tex]|D| = 0[/tex]
The critical point is at local minima