Verify each identity:

(tan x + tan y) / (1 - tan x tan y) = (sin x cos y + cos x sin y) / (cos x cos y - sin x sin y)

2people are trying different phones to see which one has the better talk time. chatlong has an average of 18 hours with a standard deviation of 2 hours and talk-a-lot has an average of 20 hours with a standard deviation of 3. the two people who tested their phones both got 20 hours of use on their phones. for the z-scores i got 1 for the chatlong company and 0 for talk-a-lot. what is the percentile for each z-score?

Which two undefined geometric terms always describe figures with no beginning or end?

What is 1.5% of 120 or what number is 1.5% of 120