Dinghy Raft
Jun/100
can som1 please help me with this maths equation?
A dinghy has sunk and the survivors are on a life raft. Their distance (in km) from a river estuary is changing as the tide goes out and comes in again. It can be moddelded by the equation d = -x^2 + 3x + 4
where x represents the number of hours since the dinghy sank.
a) how far was the dinghy from the estuary when it sank?
b) Explain what happens to the life raft in the first hour?
c) solve the equations
d) Explain what the positive soloution for this equation represents in this situation
Note: please show working out
d(x) = -x^2 + 3x + 4
a. the answer is simply d(0).
b. sketch the graph... does it curve up then down? then it goes far from the bank then gets near.
c. 0 = x^2 - 3x - 4 {equate to zero, you can also change signs.}
(x-4)(x+1) = 0
thus x = 4 or -1
thus x = 4 hrs
d. the life raft goes to the bank naturally after 4 hrs
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