Why is -LSB- math -RSB- \ cos -LRB- 30 ^ \ circ -RRB- -LSB- / math -RSB- equal to -LSB- math -RSB- \ cos -LRB- -330 ^ \ circ -RRB- -LSB- / math -RSB- ?
Why cos -LRB- -150 -RRB- is equal to + cos -LRB- 150 -RRB- and not equal to - cos -LRB- 150 -RRB- ?