(25х^2+9у^2-(5х+3у)^2):15ху
(25х^2+9у^2-(5х+3у)^2):15ху= -16/15
1) 25х^2+9у^2-(5х+3у)^2=25x^2+9y^2-25x^2-16xy-9y^2= -16xy
2) -16xy :15xy= -16/15