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 a 2 by 2 matrix may have complex entries even if "M" is a real matrix; this will be the case, in particular, if the determinant "δ" is negative. When a matrix can be expressed as real multiple of the exponent of a matrix, formula_5 then the square root is formula_6 In this case the square root is real, and can be interpreted as the square root of a type of complex number. If "M" is an idempotent matrix, meaning that "MM" = "M", then if it is not the identity matrix its determinant is zero, and its trace equals its rank which (excluding the