Test Grammar англійська мова 1) He... around the town for half an hour a) has driven b) has been driving. 2) I an eassay a) have already written b)already have written. 3) Andy... her yet a)hasn't phoned b)hasn't been phoned. 4)Sam...at six in the morning a) often wakes up b) has often waken up. 5)You...To Bristol tommorow a) are flying b) fly. 6)You look tired.You... to much a)have worked b) have been working. 7)He his camera a) has sold b) sold 8)The train... at five o'clock a) departs b) is departing. 9)Emma...the letters since ten o'clock a)has written b) has been writting. 10)The leaves from trees...in autumn a) fall down b) are falling down
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Пусть S(км)-расстояние между пунктами А и B
Течение имеет направления от пункта А к пункту B (t1<t2)
Скорость по течению равна сумме собственной скорости катера и скорости течения
V1=Vc+Vтеч
Скорость против течения равна разности собственной скорости катера и скорости течения
V2=Vc-Vтеч
V1*t1=S
V2*t2=S
Мотор выключили,значит собственная скорость катера равна 0.
V3=Vтеч
V3*t3=S
(Vc+Vтеч)*t1=S
(Vc-Vтеч)*t2=S
(Vc+Vтеч)*t1=(Vc-Vтеч)*t2
Vc*t1+Vтеч*t1=Vc*t2-Vтеч*t2
Vс*(t2-t1)=Vтеч(t1+t2)
Vc=Vтеч*()
Vтеч*(1+)*t1=S
Vтеч*()*t1=S
Vтеч*()=S
Vтеч*t3=S
t3=
t3=(2*3*6/(6-3))ч=12ч
ответ:t3=12ч
Объяснение: