Add my answer to Exercise 2.79.

Included are the following 2 files:

	Exercise_2.79.pdf
	Exercise_2.79.tm

Thank you!
							Lawrence R. Amlord
							   Jul 29th, 2013
							   Xi'an, China
Update my answer to Exercise 2.79.

Modified are the following 2 files:

	Exercise_2.79.pdf
	Exercise_2.79.tm

Thank you!
							Lawrence R. Amlord
							   Jul 29th, 2013
							   Xi'an, China
Add my answer to Exercise 2.80.

Included are the following 2 files:

	Exercise_2.80.pdf
	Exercise_2.80.tm

Thank you!
							Lawrence R. Amlord
							   Jul 29th, 2013
							   Xi'an, China