Question

A toy rocket is launched with an initial velocity of 180 m/s. The height of the rocket, in metres, can be modelled by h = –5t2 + 180t, where t is the time in seconds the rocket is in the air. How long will the rocket stay above a height of 1000 m
Answer: 22.3 s
The answer says to first put in vertex form by
h = –5t2 + 180t
h=–5(t2 –36t+324–324)
h =–5(t – 18)2 + 1620

But why is it +324. And not +(36/2)^2
Ms. Sue
324 = +(36/2)^2

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