Find the absolute maximum and absolute minimum of the function f(x,y)=2x2−4x+y2−4y+1 on the closed triangular plate bounded by the lines x=0,y=2,y=2xin the first quadrant.

Respuesta :

First check for the critical points of f by checking where the first-order derivatives vanish.

[tex]\dfrac{\partial f}{\partial x}=4x-4=0\implies x=1[/tex]

[tex]\dfrac{\partial f}{\partial y}=2y-4=0\implies y=2[/tex]

Notice how the point (1, 2) lies on the line y = 2x ; at this point, we get a value of f(1, 2) = -5 (MIN).

Next, check the points where the boundary lines intersect, which occurs at the points (0, 0), (0, 2), and (1, 2). We already checked the last one. We find f(0, 0) = 1 (MAX) and f(0, 2) = -3.

Now check on the boundary lines themselves. If x = 0, then

[tex]f(0,y)=y^2-4y+1=(y-2)^2-3[/tex]

which has a maximum value of -3 when y = 2 (so we get the same critical point as before).

If y = 2, then

[tex]f(x, 2)=2x^2-4x-3=2(x-1)^2-5[/tex]

with a maximum of -5 when x = 1.

If y = 2x, then

[tex]f(x,2x)=6x^2-12x+1=6(x-1)^2-5[/tex]

with the same maximum of -5 when x = 1.

This question is based on the absolute maximum and absolute minimum.

We get this by differentiating the terms.

Given:

f(x,y) =   [tex]2x^{2} - 4x + y^2 - 4y +1[/tex], bounded by the lines x=0,y=2,y=2x in the first quadrant,bounded by the lines x=0,y=2,y=2x in the first quadrant.

We need to determined the absolute maximum and absolute minimum of the function.

Now, partial differentiating wrt x and y.

[tex]\dfrac{\partial f}{ \partial x} = 4x -4 = 0 \Rightarrow x= 1 \\\dfrac{\partial f}{ \partial y} = 2y - 4 = 0 \Rightarrow y = 2[/tex]

Now, point (1, 2) lies on the line y = 2x ; at this point, we get a value of

f(1, 2) = -5 (MIN).

Next, check the points where the boundary lines intersect, which occurs at the points (0, 0), (0, 2), and (1, 2).

Now, find f(0, 0) = 1 (MAX) and f(0, 2) = -3.

Now check on the boundary lines themselves.

If x = 0, then we get,

[tex]f(0,y) = y^2 - 4y +1 = ( y-2)^2 -3\\[/tex]

which has a maximum value of -3 when y = 2 (so we get the same critical point as before).

If y = 2, then we get,

f(x,2) = [tex]2x^2-4x -3 = 2(x-1)^2 -5[/tex] with a maximum of -5 when x = 1.

If y = 2x, then we get,

f(x,2x) = [tex]6x^2 -12x +1 = 6(x-1)^2 -5[/tex] with the same maximum of -5 when     x = 1.

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