Which of the following is the standard equation for a circle with a center at the origin ? x^2 - y^2 = r x^2 - y^2 = r^2 x^2 + y^2 = r^2 x^2 + y^2 = r

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.