More than 500 years ago, the driving mathematician Widmer invented "+",which vividly pointed out that a vertical line was added to a horizontal plane. Later, he thought that removing the vertical was reduction, so he invented "-". 300 years later, American mathematician Audrey turned "+"half a turn and invented "×". /kloc-in the 0/8th century, Hannah, a Swiss, cut watermelon in half with one knife when distributing watermelon to children, so she invented "⊙", that is, separating two points with a line. "=" was invented by16th century British scholar Colder. He thinks that two lines with the same thickness and the same length are completely equal, which means "equality". 163 1 year, a man named harriot pulled "=" to both sides and invented the greater than sign >; Sum less than sign