Which is the equation of a hyperbola with directrices at y = ±2 and foci at (0, 4) and (0, −4)? x squared over 8 minus y squared over 16 equals 1
y squared over 16 minus x squared over 8 equals 1
x squared over 8 minus y squared over 8 equals 1
y squared over 8 minus x squared over 8 equals 1

Monitors manufactured by tsi electronics have life spans that have a normal distribution with a standard deviation of 1800 hours and a mean life span of 20,000 hours. if a monitor is selected at random, find the probability that the life span of the monitor will be more than 17,659 hours. round your answer to four decimal places.