___ ____ ___ ____
15*\/ 5 *\/ 28 *a - 7*\/ 7 *\/ 20 *a
------------------------------------
____ ___
2*\/ 35 *\/ 4 *a
(15*sqrt(5)*sqrt(28)*a - 7*sqrt(7)*sqrt(20)*a)/((2*sqrt(35)*sqrt(4)*a))