A store is thrown vertically downwards and the formula d = $16 t^{2}$ + 4t gives the distance, d metres, that it falls in t seconds. How long does it take to fall 420 metres ?

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Solution

Since, given that d=420mts.
Therefore, 420=16t²+4t
420=4(4t²+t)
105=4t²+t
0=4t²+t-105
0=4t²-20t+21t-105
0=4t(t-5)+21(t-5)
0=(4t+21)(t-5)
t=-21/4 or t=5
Therefore it will take 5 sec.

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A store is thrown vertically downwards and the formula d = 16t2 + 4t gives the distance, d metres, that it falls in t seconds. How long does it take to fall 420 metres ?

Since, given that d=420mts. Therefore, 420=16t2+4t 420=4(4t​2+t) 105=4t2+t 0=4t2+t-105 0=4t2-20t+21t-105 0=4t(t-5)+21(t-5) 0=(4t+21)(t-5) t=-21/4 or t=5 Therefore it will take 5 sec.

A store is thrown vertically downwards and the formula d = $16 t^{2}$ + 4t gives the distance, d metres, that it falls in t seconds. How long does it take to fall 420 metres ?

Since, given that d=420mts.
Therefore, 420=16t²+4t
420=4(4t²+t)
105=4t²+t
0=4t²+t-105
0=4t²-20t+21t-105
0=4t(t-5)+21(t-5)
0=(4t+21)(t-5)
t=-21/4 or t=5
Therefore it will take 5 sec.