\begin{array}{*{20}c} {x = r\cos \theta } & {r = \sqrt {x^2 + y^2 } } \\ {y = r\sin \theta } & {\theta = \tan ^{ - 1} \left( {\frac{y}{x}} \right)} \\ \end{array}
% MathType!MTEF!2!1!+- % feaafaart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn % hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB % PrgifHhDYfgasaacH8YjY-vipgYlh9vqqj-hEeeu0xXdbba9frFj0- % OqFfea0dXdd9vqai-hGuQ8kuc9pgc9q8qqaq-dir-f0-yqaiVgFr0x % fr-xfr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaqbaeqabi % GaaaqaaiaadIhacqGH9aqpcaWGYbGaci4yaiaac+gacaGGZbGaeqiU % dehabaGaamOCaiabg2da9maakaaabaGaamiEamaaCaaaleqabaGaaG % OmaaaakiabgUcaRiaadMhadaahaaWcbeqaaiaaikdaaaaabeaaaOqa % aiaadMhacqGH9aqpcaWGYbGaci4CaiaacMgacaGGUbGaeqiUdehaba % GaeqiUdeNaeyypa0JaciiDaiaacggacaGGUbWaaWbaaSqabeaacqGH % sislcaaIXaaaaOWaaeWaaeaadaWcaaqaaiaadMhaaeaacaWG4baaaa % GaayjkaiaawMcaaaaaaaa!5881!
Pasting the above "text" into MathType 5.0 will enter the above equation and make it possible to edit, save, and use in applications such as MS Word.
