11.1 – Three Dimensional Space | Mrs. Corricelli's BLOG

11.1 – Three Dimensional Space

May 15th, 2011 by corricelli

Hello,

Please use this page to discuss Chapter 11, Section 1.

3D Function Grapher: http://www.livephysics.com/ptools/online-3d-function-grapher.php

Happy blogging,
Mrs. Corricelli

8 Responses to “11.1 – Three Dimensional Space”

Colleen Lynch says:

May 31, 2011 at 3:09 pm

From the homework tonight the only question I’m alittle confused on is number 17. I’m having troubling picturing what the point is just by trying to following the description. It may because I’m confused on where the planes are but, can anyone help? I checked calc chat to see if they had an explainations but all they provided was the answer.

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Will Thomas says:

May 31, 2011 at 4:11 pm

i had a hard time with this problem too, colleen, but it helps a ton if you draw out the 3D coordinate system to try and plot the point. i pictured each plane as a wall so i could visualize the movement. when the problem says the point is 3 units behind the yz-plane, i pictured a wall standing in front of me, and then i pictured the point 3 units behind it on the x-axis, which means it has to be -3. when you picture the xz-plane as a wall and need to go 4 units to the right, you know that y is positive 4, and that z is 5 when you use the same technique for the next part of the description.

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Dustin Walsh says:

May 31, 2011 at 8:25 pm

Can someone help me with number 25 from the homework. I am having a problem visualizing the octants and which ones they are asking for, and I also checked on calc chat and it just gave the answer.

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Meg Logue says:

May 31, 2011 at 9:35 pm

Dusty, there is a really good diagram on page 810 in the book that shows each of the octets. It helps a lot to visualize them.

I had a question tho, in the back of the book it said that quadrant VII was one of the answers but wouldn’t that be greater than 0? Wouldn’t it be quadrant VII?

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Ned Wilson says:

June 1, 2011 at 7:47 am

I had the same question Meg. I thought by having the question being XY0. I’m not sure if its multiplying the x and y or is its just asking if 1 of them is negative.

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Will Thomas says:

June 1, 2011 at 2:20 pm

so, dustin, for 25, you’re supposed to find the octants in which xy<0. that means x and y must be negative or positive, but they can't both be the same. on page 810 of the book, you've got some good visuals which show the 3-dimensional space of each octant. the spaces are cubes, and the octants move counter-clockwise, starting at the lower right octant in positive z world, ending at the lower left octant in positive z world, and then picking back up at the lower right octant in negative z world, and ending at the lower left octant. for this problem, z is unimportant, since you only want to find the product of x and y that is less than 0. therefore, the octants must all be multiples of 2, and there are only 8 octants, so there are 4 answers. in the 2nd octant, x is negative, and y is positive. in the 4th octant, x is positive, and y is negative. then the 6th and 8th octants are identical to the 2nd and 4th octants, except the z has changed from a positive to a negative.

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Will Thomas says:

June 1, 2011 at 2:29 pm

so, dustin, for 25, you’re supposed to find the octants in which xy>0. that means x and y must be negative and positive, but they can’t both be the same. on page 810 of the book, you’ve got some good visuals which show the 3-dimensional space of each octant. the spaces are cubes, and the octants move counter-clockwise, starting at the lower right octant in positive z world and ending at the lower left octant in positive z world, then picking back up at the lower right octant in negative z world and ending at the lower left octant. for this problem, z is unimportant, since you only want to find the product of x and y that is less than 0. therefore, the octants must all be multiples of 2, and since there are only 8 octants, there are 4 answers. in the 2nd octant, x is negative and y is positive. in the 4th octant, x is positive and y is negative. then the 6th and 8th octants are identical to the 2nd and 4th octants, except the z has changed from a positive to a negative.

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Srinath Pingle says:

June 1, 2011 at 3:12 pm

For number 39 and 41 on tonights homework I undertsnad how to find out if they are parallel but how do you find out if they are orthoganol are not. Do you do the dot product or something?

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