Help with equation

Question

h = -16t^2 + 64t + 80

Find the exact times the firecracker is 100 feet above the ground.

 

Would I place 100 in for h then subtract it on both sides and use the quadratic formula to solve this?

Answer 1

probably twice, once on the way up and once on the way down unless shot off a hill that is at least 100 feet tall.

 

Nope, only 80 feet tall...so once on the way up and once on the way down ..

 

Move on

 

Yes plug in 100 for h

 

100 = -16t^2+64t+80

 

subtract 100 from both sides

 

0 = -16t^2+64t-20

 

Now use the quadratic formula

 

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