Multiply. Identify the product as a perfect-square trinomial, a difference of squares, or neither.
(7y + 9) (7y - 9) =
The product is (select)

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.