Вопрос школьника по предмету Алгебра
СРОЧНО!
Лодка прошла 16 км по течению реки и 18 км против течения, затратив на путь против течения на 1 ч больше, чем на путь по течению. Найдите собственную скорость лодки, если скорость течения реки составляет 1 км/ч.
Ответ учителя по предмету Алгебра
Пусть собственная скорость = х км/ч
S V t
по теч. 16км х +1 км/ч 16/(х +1) ч
пр. теч. 18 км х -1 км/ч 18/(х -1) ч
18/(х-1) — 16/(х+1) = 1
18(х +1) — 16(х -1) = (х +1)(х -1)
18х +18 -16х +16 = х² -1
х² -2х -35 = 0
по т. Виета корни 7 и -5(посторонний корень)
Ответ: V собств. = 7 км/ч
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1.Make sentences.
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3. You / live / in this town all your life?
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19. … my last birthday; 20. ……… a century;
21. … 2001.
3. Have или has.
I …. answered the question.
She ….. opened the window.
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