What is the proof the formula for cos(a+b)=cosacosb-sinasinb?

Which is an accurate comparison of the two data sets? the commute to work is typically shorter and more consistent than the commute home. the commute to work is typically shorter but less consistent than the commute home. the commute to work is typically longer and less consistent than the commute home. the commute to work is typically longer but more consistent than the commute home.