Defining the cotangent function. The cotangent function is an old mathematical function. It was mentioned in 1620 by E. Gunter who invented the notation of cotangens. Later on J. Keill (1726) and L. Euler (1748) used this function and its notation in their investigations.
Crepe Myrtles are among the toughest, most adaptable, and showiest plants that can be grown in the Texas landscape. Along with their bright colorful bloom display during the summer months the leaves of the Crepe Myrtle also turn orange, red and yellow in the fall.
These trees also get better with age, as the trunk develops a wonderful gnarled appearance, and the bark exfoliates in summer to give a gorgeous mottled look with patches of pink, grey and brown. Crepe Myrtles range from small deciduous shrubs, to trees up to about four metres, depending on the variety. Some of the older varieties are prone to powdery mildew and this can deform the blossoms, so keep an eye out for newer, more resistant varieties.