The equation $y = -6t^2 + 51t$ describes the height (in feet) of a projectile launched from the surface of Mars at 51 feet per second. In how many seconds will the projectile first reach 108 feet in height?
+128474 OK....just set the function = 108 and we have that
108 = -6t^2 + 51t rearrange as
6t^2 - 51 t + 108 = 0 divide through by 3
2t^2 - 17 t + 36 = 0 factor....if we can
(2t - 9 ) (t - 4) = 0
Set both factors to 0 and solve for t and we get two times
t = 9/2 sec and t = 4 sec
So 9/2 sec is correct....
