polar coordinates -> cartesian coordinate system ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg21394] polar coordinates -> cartesian coordinate system ?*From*: "Guybrush Threepwood" <guybrush_ at gmx.de>*Date*: Mon, 3 Jan 2000 03:12:26 -0500 (EST)*Organization*: bingo e.V. (Buergernetz Ingolstadt e.V.)*Sender*: owner-wri-mathgroup at wolfram.com

Hello Using the polar coordinate system you can calculate the area with the formula: 1/2 * Integral [t1,t2] of r^2 d(). Apparently you can convert that to the cartesian coordinate system so that finally theres a formula like: 1/2 * Integral[t1,t2] of y'*x - x'*y. Could anyone tell me how to convert the first formula to the second one ? Btw in polar coordinates r^2 = x^2 + y^2 !! ok thanks