Рак-велосипедист проехал от деревни до города со скоростью 15 км/ч, а возвращается со скоростью 10 км/ч. Какова средняя скорость рака-велосипедиста?

Решение.
Пусть расстояние от деревни до города - s км. Тогда в город рак-велосипедист доехал за s / 10 ч. Всего велосипедист затратил s / 6 ч:
s / 15 + s / 10 = s / 6.
Следовательно, его средняя скорость равна: 2s : (s / 6) = 12 (км/ч). Ответ: Средняя скорость рака-велосипедиста 12 км/ч.

№1

а) (-0,75; 2,75)

б) (0,1875; -5,25)

 

№2

б) n=2/3, m=1/3

в) z=3. y=-0.6

 

6m-9n=-4

2m+5n=4 / * -3

 

6m-9n=-4

-6m-15n=-12

способ сложения

 

-9n-15n=-4-12

-24n=-16

n=2/3

 

2m+5n=4

2m+5*2/3=4

m=1/3

 

 

б) 5y+8z=21  / * -2

      10y-3z=-15

 

    -10y-16z=-42

      10y-3z=-15

      способ сложения

 

      -16z-3z=-42-15

        -19z=-57

          z=3

 

      5y+8z=21

      5y+8*3=21

      5y=21-24

      5y=-3

      y=-0.6

 

 

 

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