SOLUTION: A rock is thrown from the top of a tall building. The distance d, in feet, between the rock and the ground t seconds after it is thrown is given by d= -16t^2-4t+432. How long afte

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Question 431119: A rock is thrown from the top of a tall building. The distance d, in feet, between the rock and the ground t seconds after it is thrown is given by
d= -16t^2-4t+432. How long after the rock is thrown is it 300 feet from the ground?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+d=+-16t%5E2+-+4t+%2B+432+
+300+=+-16t%5E2+-4t+%2B+432+
+-16t%5E2+-+4t+=+-+132+
+16t%5E2+%2B+4t+-+132+=+0+
++4t%5E2+%2B+t+-+33+=+0+
+t+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
+a+=+4+
+b+=+1+
+c+=+-33+
+t+=+%28-1+%2B-+sqrt%28+1%5E2-4%2A4%2A%28-33%29+%29%29%2F%282%2A4%29+
+t+=+%28-1+%2B-+sqrt%28+1++%2B+528+%29%29+%2F+8+
+t+=+%28-1+%2B-+23%29+%2F+8+
+t+=+-3+ (can't use this)
+t+=+11%2F4+
The rock is 300 ft from the ground
when t = 2.75 sec