SOLUTION: At the start of the basketball game, the referee tosses a ball for a jump ball. The equation that models the height of the ball is h(t) = -16t2 + 24t + 5 During what time interv

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Question 619125: At the start of the basketball game, the referee tosses a ball for a jump ball. The equation that models the height of the ball is
h(t) = -16t2 + 24t + 5
During what time interval is the height of the ball above 9 feet? (Round your answer to the nearest tenth of a second.)
a) .5 seconds to 2.1 seconds
b) .4 seconds to 1.9 seconds
c) .6 seconds to 1.8 seconds
d) .2 seconds to 1.3 seconds
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
It reaches 9 ft going up and coming back down
+9+=+-16t%5E2+%2B+24t+%2B+5+
+-16t%5E2+%2B+24t+-+4+=+0+
+-4t%5E2+%2B+6t+-+1+=+0+
Use the quadratic formula
+t+=+%28-b+%2B-+sqrt%28+b%5E2+-+4%2Aa%2Ac+%29%29+%2F+%282%2Aa%29+
+t+=+%28-6+%2B-+sqrt%28+6%5E2+-+4%2A%28-4%29%2A%28-1%29+%29%29+%2F+%282%2A%28-4%29%29+
+t+=+%28-6+%2B-+sqrt%28+36+-+16+%29%29+%2F+%28+-8+%29+
+t+=+%28-6+%2B-+sqrt%28+20+%29%29+%2F+%28+-8+%29+
+t+=+%28-3+%2B-+sqrt%28+5+%29%29+%2F+%28+-4+%29+
I think the answer is (d)