X + y = 12
x^2/y + y^2/x = 18
x^3 + y^3 = 18xy
(x+y)(x^2-xy+y^2) = 18xy
12(x^2-xy+y^2) = 18xy
2x^2 - 2xy + 2y^2 - 3xy = 0
x^2 - 5/2xy + y^2 = 0
x^2 - (2 + 1/2)xy + (2 * 1/2)y^2 = 0
(x - 2y)*(x - y/2) = 0
x + y = 12, x = 2y -> x = 8, y = 4
x + y = 12, y = 2x -> x = 4, y = 8
1) находим производную 5(х+5)^4/(x+5)^5-5=5/(x+5)-5
Длина плота в 2 раза больше, => длину умножим на 2: x * 2 или 2x.
………=3/2(у+3) +(у^2 -у-3)/((у+3)(у-3)) - 1=(3у-9+2у^2-2у-6-2у^2+18)/2(у^2-9)=(у+3)/(2(у+3)(у-3))=1/2у-6
при у=7,7
1/(2*7,5-6)=1/9