Dandelion coffee In 1919, dandelion root was noted as a source of cheap 'coffee'. It has also been part of edible plant classes dating back at least to the 1970s. Harvesting dandelion roots requires differentiating 'true' dandelions ("Taraxacum" spp.) from other yellow daisy-like flowers such as catsear and hawksbeard. True dandelions have a ground-level rosette of deep-toothed leaves and hollow straw-like stems. Large plants that are 3–4 years old, with taproots approximately 0.5 inch (13 mm) in diameter, are harvested for dandelion coffee. These taproots are similar in appearance to pale carrots. After harvesting, the dandelion roots are dried, chopped, and roasted.
Square root of numbers, called the complex numbers, that does contain solutions to the square root of a negative number. This is done by introducing a new number, denoted by "i" (sometimes "j", especially in the context of electricity where ""i"" traditionally represents electric current) and called the imaginary unit, which is "defined" such that . Using this notation, we can think of "i" as the square root of −1, but notice that we also have and so −"i" is also a square root of −1. By convention, the principal square root of −1 is "i", or more generally, if "x" is