Åk 6–9

English/Svenska
 1.2 History Addition (+) and Subtraction (-) The first of the four arithmetic operators that we find in history is addition. To solve tasks with addition, tools like the abacus (or counting frame) were used, and the Inca people even used threads in different colors onto which they tied knots.    The oldest of the arithmetic operators, which is known of, is the subtraction sign: . It was discovered in Egypt on a papyrus roll.  The sign "+" and "–" come from when people harvested different grains and stored them in sacks. There was a sack that everyone compared the weight with, and if any sack weighed more or less than this sack, it was given a plus or minus.  Multiplication (·) and Division (÷) When the numbers created by multiplication became large, more tools were needed to handle this. The Greeks used Pythagorean tables; the Babylonians used square root tables, and the Chinese, the abacus. The Romans had a very hard time with multiplication with their Roman numerals.  1632 used the symbol "x" for multiplication for the first time.    The Babylonians and the Indians were the first that used division and had names for every element, element – dividend, divisor and quotient, words that we still use today. The Arabs brought with them division to Europe during the Middle Ages. In 1202, Leonardo de Pisa presented a way of expressing division which entailed writing the numbers in a row instead of in fraction form. A mathematician by the name Oughtred began using the symbol ":" for division in 1647. Powers (x²) and Roots (√) The first peoples to use powers were the Babylonians. We know this because we have found clay tablets with mathematical calculations on the banks of the Euphrates River.   The Arabic countries learned to count roots from the Indians which were called "gidir" which was a translation from the sanscrit word "mula" which means plant or root. "Varga mula" means ”the square root of”.  The word root – roots comes from the Latin word "radix" or "radicis" which means roots.   Equal to (=) , Greater Than (>) and Less Than (<) The equals sign was first written by Robert Recorde in his book, "The Ground of Arts", published in London in 1582.  During the 1700’s, the greater than symbol " >" and less than symbol " <" were used for the first time.