The expression cos(a-b) - cos(a+b) is equal to

1) -2sinasinb
2) -2cosb
3) 2cosacosb
4) 2sinasinb

so far, all i've gotten is

cosxcosy + sinxsiny - cosxcosy - sinxsiny

i don't know where to go from there. i'm assuming that's zero, and i don't know which of the others equal they all look the same.

Choose the point slope form of the equation below that represents the like that passes through the points (-6,4) and (2, 0)

What function has a range {yly< 5}? question on picture above^

Assume that there is a 11% rate of disk drive failure in a year. a. if all your computer data is stored on a hard disk drive with a copy stored on a second hard disk drive, what is the probability that during a year, you can avoid catastrophe with at least one working drive? b. if copies of all your computer data are stored on four independent hard disk drives, what is the probability that during a year, you can avoid catastrophe with at least one working drive?