WHEN Charlotte Hobbs decided to teach her 11-year-old pupil about the imaginary maths needed to work out the square root of a negative number, she knew it would be a stretch.
But then mathematicians defined the square root of negative one as a new number called i, opening up a whole new mathematical world of complex numbers.
但后来数学家们取 -1 的平方根为一个叫 i 的新数字,在数学领域里,这为复杂数字打开了全新的世界。
It is, though, a totally different kind of mental effort from plugging lots of numbers into complicated square root formulas and ultimately, much more worthwhile.