SOLUTION: s=-16t^2+32t+40. How did they get from there calcuating in .5 seconds to -4+16+40? Where did the -4 come in. When I did the problem I got 64+32+40. What I do wrong?

Question 205116: s=-16t^2+32t+40. How did they get from there calcuating in .5 seconds to -4+16+40? Where did the -4 come in. When I did the problem I got 64+32+40. What I do wrong?
Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
s=-16t^2+32t+40. How did they get from there calcuating in .5 seconds to -4+16+40? Where did the -4 come in. When I did the problem I got 64+32+40. What I do wrong?
---------
-16t^2 at t = 0.5
= -16(0.25)
= -4
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