William Anthony Granville, Elements of the Differential and Integral Calculus… (1911)
“ Law of Cosines. 47. distance between points and . 48. distance from line to . 49. ; coördinates of middle point. 50. ; transforming to new origin . 51. ; transforming to new axes making the angle with old. 52. ; transforming from rectangular to polar coördinates. ”
