Найдите значение выражения а^2+в^2,если а+в=7,ав=12 - Знания.site

Найдите значение выражения а^2+в^2,если а+в=7,ав=12
- Предмет:
  Алгебра
- Автор:
  arielleatkins
- 4 года назад

Ответы 2

a = 3, b = 4,a^2 + b^2 = 9 + 16 = 25
- Автор:
  celestes4l1
- 4 года назад
- 0
a²+b²=(a+b)²-2ab=7²-2*12=49-24=25
- Автор:
  graciechang
- 4 года назад
- 0
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Man has never been satisfied with simply talking. For some reason he has always considered his words and ideas to be so important that he has forever tried to find ways of recording them on paper. Just as man has developed so many systems of writing, so he has also developed various tools with which to write.

One of the first instruments developed by man for writing was the stylus. This was a sharp instrument made of bone or metal and with it the writer could scratch his message onto stone or wood. It was used for thousands of years and was very practical: it could also be used as a weapon. Julius Caesar was killed with one in 44 BC.

The ideas of a pen and ink were developed by the Egyptians. Their version of the pen was made from bamboo. They sharpened one end of the stem to make a nib; that is the point with which you actually write. They then filled the hollow part of the stem with ink and squeezed it to force the ink onto the nib. It was a good idea but, as you can imagine, when paper was later introduced, a much finer instrument was needed.

The problem was solved with the introduction of the quill pen. The quill is one of the large feathers on the wing or tail of a swan or goose. The quill also gave us the word "pen". You see, feather in Latin is "penna". However, because this pen was in fact a feather, it had to be sharpened quite often and so a special instrument was made for this purpose - the penknife.

The quill was used from the 6th to the 18th centuries, and then in the 19th century a machine was invented which successfully made a nib out of metal and this could then be fitted into a holder and dipped into a bottle of ink. Finally, in 1884, a young American, Lewis Waterman, found a way of putting the ink into the holder and the fountain pen as we know it was completed.

Although the fountain pen was very popular, a new kind of pen was introduced just before the Second World War, which became more popular. This was the ball pen or as a lot of people calls it, the biro. It was developed by a Hungarian living in Argentina whose name was, interestingly enough, Joseph Biro.

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d. As soon as he learnt how to make paper.

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d. cut the tail off a swan.

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Answer the following questions with a phrase or a sentence.

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6. Who made the very first version of the fountain pen?

7. What were the disadvantages of the quill pen?

8. Where does the word biro come from?
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