Предмет: Математика, автор: Ordo

Из двух пунктов А и В расстояние между которыми равно 21 км одновременно навстречу друг другу два велосипедиста и встретились через час.Если бы 2 выехал из пункта В на 35 минут позже, чем первый из А, то они встретились бы на расстоянии 9 км от пункта В. Найдите скорость второго велосипедиста, если они оба двигались с постоянными скоростями

Ответы

Автор ответа: Slider808

Скорость сближения = 21/1=21 км/час

Скорость первого х

Второго 21-х

Первый за 35 мин(7/12)часа проехал

х*7/12

Потом до встречи первый проехал х*t

второй проехал 9 км за время t=9/(21-х)

Значит все расстояние

х*7/12+х*t+9=21

x*7/12+x*9/(21-x)-12=0

x*7*(21-x)+x*9*12-144*(21-x)=0

147x-7x^2+108x+144x-3024=0

7x^2-399x+3024=0

x^2-57x+432=0

D=3249-1728=1521=39^2

x=(57-39)/2=9 км\ч - скорость первого

21-9=12 км\ч - скорость второго

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