He equation $y=-16t^2+22t+45$ describes the height (in feet) of a ball thrown upwards at $22$ feet per second from $45$ feet above the ground. find the time (in seconds) when the ball will hit the ground. express your answer as a common fraction.

hello from mrbilldoesmath!

answer:

a(n) - a(n-1) -3

discussion:

this ones a bit interesting. given a(n) = 5 - 3n consider this:

a(n-1) = 5 - 3(n-1)

          = (5 - 3n) + 3             => but a(n) = 5 - 3n, the first term

          = a(n)   + 3                 => subtract 3 from both sides

a(n-1) -3 = a(n)  

or

a(n) - a(n-1) -3

you,

mrb

hope this .

r3t40