Italy- in Europe, Argentina- America
Brazil-America
Japan- Asia
Mexico-America
China-Asia
Portugal-Europe
Egypt-Africa
Russia-Europe, Asia
England-Europe
France-Europe
Spain-Europe
Turkey-Africa
Greece-Europe
the USA-America
Hungary- Europe
1) 6+8=14(мин)-время на одно платье
2) 14*8=112(мин)-на восемь платьев
Ответ: 112 минут было затрачено на восемь платьев.
P.S.В решение не уверена поскольку, задача была странно задана.
1) a+b= -3,6
2) |a|+b= 9
3) |a+b|= 3,6
4)|a|+|b|=9
Первый способ:
![$\LARGE\\ x*y^2-y*lnx=3\\ (x*y^2)'-(y*lnx)'=(3)'\\ (x)'*y^2+x*(y^2)'-(y)'*\ln{x}-(\ln{x})'*y=0\\ y^2+2xyy'-y'*\ln{x}-{y\over x}=0\\ y'(2xy-\ln{x})+y^2-{y\over x}=0\\ y'={{y\over x}-y^2\over 2xy-\ln{x}}\\ y'=-{y^2-{y\over x}\over 2xy-\ln{x}}$](https://tex.z-dn.net/?f=+%24%5CLARGE%5C%5C+x%2Ay%5E2-y%2Alnx%3D3%5C%5C+%28x%2Ay%5E2%29%27-%28y%2Alnx%29%27%3D%283%29%27%5C%5C+%28x%29%27%2Ay%5E2%2Bx%2A%28y%5E2%29%27-%28y%29%27%2A%5Cln%7Bx%7D-%28%5Cln%7Bx%7D%29%27%2Ay%3D0%5C%5C+y%5E2%2B2xyy%27-y%27%2A%5Cln%7Bx%7D-%7By%5Cover+x%7D%3D0%5C%5C+y%27%282xy-%5Cln%7Bx%7D%29%2By%5E2-%7By%5Cover+x%7D%3D0%5C%5C+y%27%3D%7B%7By%5Cover+x%7D-y%5E2%5Cover+2xy-%5Cln%7Bx%7D%7D%5C%5C+y%27%3D-%7By%5E2-%7By%5Cover+x%7D%5Cover+2xy-%5Cln%7Bx%7D%7D%24+)
![\\](https://tex.z-dn.net/?f=%5C%5C)
Второй способ через частные производные:
![$\LARGE\\x*y^2-y*\ln{x}=3\\\\ F'_x=\frac{\partial F}{\partial x}=y^2-{y\over x}\;\;\;\;\;\; F'_y=\frac{\partial F}{\partial y}=2xy-\ln{x}\\\\ y'=-{F'_x\over F'_y}=-{y^2-{y\over x}\over 2xy-\ln{x}}$](https://tex.z-dn.net/?f=+%24%5CLARGE%5C%5Cx%2Ay%5E2-y%2A%5Cln%7Bx%7D%3D3%5C%5C%5C%5C+F%27_x%3D%5Cfrac%7B%5Cpartial+F%7D%7B%5Cpartial+x%7D%3Dy%5E2-%7By%5Cover+x%7D%5C%3B%5C%3B%5C%3B%5C%3B%5C%3B%5C%3B+F%27_y%3D%5Cfrac%7B%5Cpartial+F%7D%7B%5Cpartial+y%7D%3D2xy-%5Cln%7Bx%7D%5C%5C%5C%5C+y%27%3D-%7BF%27_x%5Cover+F%27_y%7D%3D-%7By%5E2-%7By%5Cover+x%7D%5Cover+2xy-%5Cln%7Bx%7D%7D%24+)