Merge pull request #8 from guangmingyao/yao_dev

Yao dev - updating the Friday lecture on basis and dimension
minor change on week7 day 2 notes
Changed the lecture on determinants. Added clicker quizzes for sections 1 and 2 and removed the third clicker quiz.
Made changes to the section on linear combinations of vectors.
minor changes on week 7 day 3 ntoes
Copied slides on vector spaces over to the next day on span and basis.
Merge pull request #14 from KellyBlack/black_dev

Black dev - added slides on vector space to the slides on basis and span
Added images for the spring mass system.
Made changes to the constant coefficient linear equations lecture.
Changed the main file for the notes to print out the lecture on spans and linear independence.
Merge pull request #15 from KellyBlack/black_dev

Black dev made changes to the lecture on constant coefficient linear equations
minor changes on week 8 day 1 notes
Merge remote-tracking branch 'origin/black_dev' into yao_dev
Fixed slides for the class on solving 2nd order DEs.
Merge pull request #16 from KellyBlack/black_dev

Fixed slides for the class on solving 2nd order DEs.
Added solutions for matrices.tex.
modified spanOfVectors
minor change
Cleaned up the lecture on complex roots for constant coef. equations.
Changed the name of realroots to complexroots.