При яких значеннях x i z вектори a(3; 2; 4) i b(x; -5; z) колінеарні?

векторы коллинеарны, если отношения их координат равны.

ответ: при х = -7,5;   z = -10.

Since birth, most of my days are spent in the city. Only rarely did I manage to go on vacation to other countries or somewhere, as they say, in nature. Therefore, most of my impressions of nature are actually connected with these rare trips and many different documentaries and TV shows about nature.

Perhaps I know even more about different plants and animals than people who have been living in villages and villages and even in forests all the time. However, I have no idea how to feel nature, how many natural phenomena look like and the like. My nature lies in the noise of cars in the morning, tigers, zebras and leopards are different brands of cars in the stone jungle, even the cycles of night and day are replaced by street lighting and lanterns, the work of heavenly bodies is not so significant.

My nature is limited to street cats and dogs that can be found on a walk or when visiting a city cafe or museum. I travel by nature in underground underground and on buffaloes and rhinoceros - buses and trolleybuses. Sometimes it is possible to use the giant tramway track.

I do not know at all how to distinguish poisonous berries from edible ones or the sounds of different animals, nevertheless, I am well versed in the signs of communication salons, banks and I know where it is more profitable to get food - in which cafes there are promotions and which shops give discounts. I do not know how to navigate the weather signs, but I know perfectly well when to expect traffic jams in the city and can determine the approximate intellectual level of the owner of this wardrobe set by the clothes.

For modern man, nature is something else, not at all what it was for people just a century earlier. We become less dependent, but also more distant from nature, we live in a completely different space, which is subject to its own mechanisms and characteristics. Probably, people like me, who most of their time live in the metropolis, in the space of the concrete jungle, are changing especially.

Real nature with animals and plants looks to me like some kind of legend from fairy tales. Such nature is known to me only from video and photos, as a distant world that will remain unknown.

Source: Essays about nature

Пусть х - скорость первого автомобиля относительно земли. пусть у - скорость второго автомобиля относительно земли. х-у=20 в случае, когда машины догоняют друг друга. х+у=100 в случае, когда машины едут навстречу друг другу. х-у=20 х+у=100 выразим в первом уравнении х через у: х=у+20 и подставим во второе уравнение: у+20+у=100 2у=100-20 2у=80 у=80: 2 у=40 км/ч - скорость второго автомобиля относительно земли. подставим это значение у в первое уравнение: х-у= 20 х-40=20 х=20+40 х=60 км/ч - скорость первого автомобиля относительно земли. ответ: 60 км/ч; 40 км/ч