Area of a circle trigonometry, uses the coarea formula. Define a function formula_10 by formula_11. Note ρ is a Lipschitz function whose gradient is a unit vector formula_12 (almost everywhere). Let "D" be the disc formula_13 in formula_14. We will show that formula_15, where formula_16 is the two-dimensional Lebesgue measure in formula_14. We shall assume that the one-dimensional Hausdorff measure of the circle formula_18 is formula_19, the circumference of the circle of radius "r". (This can be taken as the definition of circumference.) Then, by the coarea formula, Similar to the onion proof outlined above, we could exploit calculus in a different way in
Straight from the Hart Straight from the Hart Straight from the Hart is a 2011 autobiography by Canadian professional wrestler Bruce Hart. The book chronicles Hart's childhood in Calgary as a member of the Albertan Hart wrestling family, his career in the wrestling industry to his later life as a trainer. It was published by ECW Press. The book is one of a long line of books by or about members of Hart's family. The book was first announced in May 2010. In March Hart was interviewed about the book on WDFN Wrestling Elite and Monday Night Mayhem. On Monday Night Mayhem Hart explained