Assignment 22

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course MTH 272

Resubmitted on 12/17 about 2:40 pm

***This is a resubmission***022.

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Question: `qQuery problem 7.1.24 picture of sphere, diam from (-1,-2,1) to (0, 3, 3).

What is the standard form of the equation of the pictured sphere?

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Your solution:

(h,k,l)= (-1+0)/2 , (-2+3)/2 , (1+3)/2 = (-1/2,1/2,2) this is the center of the sphere.

To find the radius:

R=sqrt.((0- -1/2)^2 + (3- 1/2)^2 + (3-2)^2) = sqrt(1/4 + 25/4 + 1) = sqrt. (30/4) = sqrt.(15/2)

R=sqrt.(15/2) = sqrt((x+ 1/2)^2 + (y- 1/2)^2 + (z-2)^2) square both sides

(x+ 1/2)^2 + (y- 1/2)^2 + (z-2)^2 = 15/2

confidence rating #$&*:3

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Given Solution:

`a The midpoint between (-1, -2, 1) and (0, 3, 3) is (-1/2, 1/2, 2).

Thus the sphere will have the form (x - (-1/2) )^2 + (y - 1/2)^2 + (z-2)^2 = r^2.

r is half the diameter, which is half of `sqrt( (0 - -1)^2 + (3 - -2)^2 + (3 - 1)^2 ) = `sqrt(1+25+4) = `sqrt(30). The radius is therefore `sqrt(30) / 2 and r^2 = 30 / 4 = 15/2.

The equation is therefore (x - (-1/2) )^2 + (y - 1/2)^2 + (z-2)^2 = 15/2.

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Self-critique (if necessary):OK

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Self-critique Rating:OK

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Question: `qQuery problem 7.1.39 (was 7.1.38) yz-trace of x^2 + y^2 + z^2 - 6x - 10 y + 6 z + 30 = 0

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Your solution:

To solve, x will equal zero. So we have

(y^2 -10y) + (z^2+6z) + 30 = 0

(y^2-10y+25) + (z^2+6z+9) +30 - 25 - 9 = 0

(y-5)^2 + (z+3)^2 -4 = 0

(y-5)^2 + (z+3)^2 = 4 r^2=4 so r=2

The yz trace is a circle with center (0,5,-3) and radius 2.

confidence rating #$&*:3

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Given Solution:

`a The yz trace is characterized by x = 0.

The equation of the y-z trace is therefore y^2 - 10 y + z^2 + 6z + 30 = 0.

This is the equation of a circle in the y-z plane. Completing the square we get

(y^2 - 10 y + 25 - 25) + (z^2 + 6 z + 9 - 9) + 30 = 0 or

(y-5)^2 + (z+3)^2 = 4 or

(y-5)^2 + (z+3)^2 = 2^2.

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Self-critique (if necessary):OK

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Self-critique Rating:OK

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Question: `qWhat is the equation of the yz-trace of the given sphere and what shape does this equation define in the y-z plane?

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Your solution:

To solve, x will equal zero. So we have

(y^2 -10y) + (z^2+6z) + 30 = 0

(y^2-10y+25) + (z^2+6z+9) +30 - 25 - 9 = 0

(y-5)^2 + (z+3)^2 -4 = 0

(y-5)^2 + (z+3)^2 = 4 r^2=4 so r=2

The yz trace is a circle with center (0,5,-3) and radius 2.

confidence rating #$&*:3

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.............................................

Given Solution:

`a `a The yz trace is characterized by x = 0.

The equation of the y-z trace is therefore y^2 - 10 y + z^2 + 6z + 30 = 0.

This is the equation of a circle in the y-z plane. Completing the square we get

(y^2 - 10 y + 25 - 25) + (z^2 + 6 z + 9 - 9) + 30 = 0 or

(y-5)^2 + (z+3)^2 = 4 or

(y-5)^2 + (z+3)^2 = 2^2.

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Self-critique (if necessary):OK

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Self-critique Rating:OK

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Question: `qWhat is the center and what is the radius of the circle?

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Your solution:

To solve, x will equal zero. So we have

(y^2 -10y) + (z^2+6z) + 30 = 0

(y^2-10y+25) + (z^2+6z+9) +30 - 25 - 9 = 0

(y-5)^2 + (z+3)^2 -4 = 0

(y-5)^2 + (z+3)^2 = 4 r^2=4 so r=2

The yz trace is a circle with center (0,5,-3) and radius 2.

confidence rating #$&*:3

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

.............................................

Given Solution:

`a `a The yz trace is characterized by x = 0.

The equation of the y-z trace is therefore y^2 - 10 y + z^2 + 6z + 30 = 0.

This is the equation of a circle in the y-z plane. Completing the square we get

(y^2 - 10 y + 25 - 25) + (z^2 + 6 z + 9 - 9) + 30 = 0 or

(y-5)^2 + (z+3)^2 = 4 or

(y-5)^2 + (z+3)^2 = 2^2.

We thus have a circle of radius 2, in the y-z plane, centered at (0, 5, -3).

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Self-critique (if necessary):OK

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Self-critique Rating:OK

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Question: `qQuery Add comments on any surprises or insights you experienced as a result of this assignment.

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Question: `qQuery Add comments on any surprises or insights you experienced as a result of this assignment.

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Self-critique rating:

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