Question

Proszę o obliczenie(układ równań) i możlwe wytłumaczenie: {240=v*t {240=(v+20)*(t-1)

Answer 1

v*t = 240  => t = 240/v

( v + 20)*( t - 1) = 240

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t = 240/v

v*t - v + 20 t - 20 = 240

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t = 240/v

240 - v + 20*[ 240/ v] - 20 = 240

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t = 240/v

- v + 4800/v - 20  = 0  / * v

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t = 240/v

- v^2 + 4 800 - 20 v = 0

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t = 240/v

v^2 + 20 v - 4 800 = 0

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delta = 20^2 - 4*1*( -4800) = 400 + 19 200 = 19 600

p (delty) = 140

v = [ - 20 + 140]/2 = 120/2 = 60

oraz

t = 240 /60 = 4

Odp. v = 60 km/h,  t = 4 h.

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