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Set up an integral of the form
dc h2(y) h1(y) f(x,y) dx dy
for the volume of the region enclosed by the surfaces z = 2 - x2 - y2 and z = 2x + 2y. What is h2(0)+f(0,0)?
A. 5.
B. 13 + 2.
C. V2+1.
D. V3+1.
E. V2 + 2.


Sagot :

Answer:

Option D.

[tex]\mathbf{\sqrt{3}} +1}[/tex]

Step-by-step explanation:

The given integral is:

[tex]\int^d_c \int ^{h_2(y)}_{h_1(y)} f(x,y)\ dx \ dy[/tex]

The intersection curves enclosed by the surfaces:

z = 2 - x² - y² and z = 2x + 2y

This implies that:

[tex]2x +2y = 2 - x^2- y^2[/tex]

[tex](x^2 + 2x) +(y^2 + 2y) = 2 \\ \\ (x+1)^2 + (y + 1)^2 = 4 --- (1)[/tex]

We will realize that the curve of this intersection is a circle which is centered at (-1, -1) of the radius 2.

So, from equation (1)

[tex](x + 1)^2 = 4 - (y + 1)^2[/tex]

x + 1 = ±[tex]\sqrt{4 - (y + 1)^2}[/tex]

[tex]x = -1 \pm \sqrt{4 - (y+1)^2}[/tex]

Now,

[tex]h_2 (y) = -1 + \sqrt{4 - (y +1)^2}[/tex] and [tex]h_1 (y) = -1 - \sqrt{4 - (y +1)^2}[/tex]

[tex]h_2(0) = -1 + \sqrt{4-1}[/tex]

[tex]h_2(0) = -1 + \sqrt{3}[/tex],  and:

[tex]At \ \ (-1, -1); \\ \\ z = 2 - (-1)^2 - (-1)^2 \\ \\ z = 2 - 1 - 1 \\ \\ z = 0[/tex]

and

[tex]z = 2x + 2y \\ \\ z = 2(-1) + 2 (-1) \\ \\ z = -2 + (-2) \\ \\ z = -4[/tex]

The surface z = 2-x²-y² lies above z = 2x + 2y in the region of intersection

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

So, h₂ (0) + f(0,0) = [tex]\sqrt{3}} - 1 + 2[/tex]

h₂ (0) + f(0,0) = [tex]\mathbf{\sqrt{3}} +1}[/tex]