SOLUTION: The height in feet for a ball thrown upward at 48 feet per second is given by s(t) = -16t^2 + 48t, where t is the time in seconds after the all is tossed. What is the maximum heigh

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons -> SOLUTION: The height in feet for a ball thrown upward at 48 feet per second is given by s(t) = -16t^2 + 48t, where t is the time in seconds after the all is tossed. What is the maximum heigh      Log On


   



Question 847122: The height in feet for a ball thrown upward at 48 feet per second is given by s(t) = -16t^2 + 48t, where t is the time in seconds after the all is tossed. What is the maximum height that the ball will reach?
What is the method of the quadratic formula used to solve this problem?

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Analyze the quadratic formula a little
+t+=+%28-b+%2B-+sqrt%28+b%5E2+-+4%2Aa%2Ac+%29%29+%2F+%282%2Aa%29+
You can break this up into 2 parts, both of which are true:
+t%5B1%5D+=+%28-b+%2B+sqrt%28+b%5E2+-+4%2Aa%2Ac+%29%29+%2F+%282%2Aa%29+
and
+t%5B2%5D+=+%28-b+-+sqrt%28+b%5E2+-+4%2Aa%2Ac+%29%29+%2F+%282%2Aa%29+
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Now show it this way:
+t%5B1%5D+=+-b%2F%282a%29+%2B+sqrt%28+b%5E2+-+4%2Aa%2Ac+%29+%2F+%282%2Aa%29+
and
+t%5B2%5D+=+-b%2F%282a%29+-+sqrt%28+b%5E2+-+4%2Aa%2Ac+%29+%2F+%282%2Aa%29+
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What these last 2 equations are saying is that one
of the roots is this far +sqrt%28+b%5E2+-+4%2Aa%2Ac+%29+%2F+%282%2Aa%29+
in one direction, and the other root is this far
+sqrt%28+b%5E2+-+4%2Aa%2Ac+%29+%2F+%282%2Aa%29+ in the opposite direction
with +-b%2F%282a%29+ right in the middle.
So, +-b%2F%282a%29+ is the t-coordinate of the max or the min
( exactly 1/2 way between the roots )
--------------------------------
With your problem:
+s%28t%29+=+-16t%5E2+%2B+48t+
+a+=+-16+
+b+=+48+
+t%28max%29+=+-b%2F%282a%29+
+t%28max%29+=+-48%2F%28+2%2A%28-16%29%29+
+t%28max%29+=+48%2F32+
+t%28max%29+=+1.5+
Now plug this back into your equation
to get +s%28max%29+
+s%28max%29+=+-16%2A1.5%5E2+%2B+48%2A1.5+
+s%28max%29+=+-16%2A2.25+%2B+72+
+s%28max%29+=+-36+%2B+72+
+s%28max%29+=+36+ ft
Here's the plot:
+graph%28+400%2C+400%2C+-1%2C+4%2C+-5%2C+40%2C+-16x%5E2+%2B+48x+%29+