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Find the critical points of the given function and then determine whether they are local maxima, local minima, or saddle points.
f (x, y) = x^2 + y^2 + 2xyf(x,y)=x 2 +y 2 +2xy


Sagot :

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