117b – Homework 4

Due Thursday, February 1 at 1:00 pm.

The second pdf contains some hints for problem 3.

7 Responses to 117b – Homework 4

1. Jed says:

I believe there to be a typographical error in the definition of the \otimes product for 1d. Specifically, x_4y_3 term should carry a negative sign.

2. Domenic says:

Also, maybe this is something way basic for everyone versed in topology, but it would be nice for me if you could clarify that the disks are open. I eventually just said, in part (e), “we must have C be an open disk; this does not change the area, so all important properties are preserved, but the openness will be required later.”

Now to prove… 1e, 2, and 3. Woohoo…

3. Jed,

I think you may be right. Writing a vector (a,b,c,d) as
a + bi + cj + dk the multiplication table should be

i^2=j^2=k^2= -1

ij=-ji=k

jk=-kj=i

ki=-ik=j

4. Domenic,

Yes, the disk in part (g) -not (e)- is supposed to be open. Although this really doesn’t matter.

5. Domenic says:

No idea what the bracket notation in the hint is supposed to mean. Floor? Ceiling? Round to nearest? Stuff in to a matrix and then take the determinant? Yeah… not much of an issue since I can’t seem to prove the identity anyway (50 more minutes to go!), but yeah.

6. The bracket notation is the integer part (floor) function. It is the same notation used in lecture. (Edited.)

7. Domenic says:

I must be doing something wrong then, since I have isolated additive terms u and z in the expansion. The fact that there are extra terms besides just u and z means that the ceiling must be > u + z, since any extra contribution besides u and z will push it up by at least 1.