Lagrange
L = 75·x + 70·y + k·(15·x^2 + 71·x·y + 10·y^2 - 3452)
Partiell ableiten
Lx = 30·k·x + 71·k·y + 75 = 0 --> k = - 75/(30·x + 71·y)
Ly = 71·k·x + 20·k·y + 70 = 0 --> k = - 70/(71·x + 20·y)
k gleichsetzen
- 75/(30·x + 71·y) = - 70/(71·x + 20·y)
y = 645/694·x
In Nebenbedingung einsetzen
15·x^2 + 71·x·y + 10·y^2 - 3452 = 0
15·x^2 + 71·x·(645/694·x) + 10·(645/694·x)^2 - 3452 = 0
x = 6.206136807
y ausrechnen
y = 645/694·x
y = 645/694·6.206136807 = 5.767951355
Kosten ausrechnen
K = 75·x + 70·y
K = 75·6.206136807 + 70·5.767951355 = 869.2168553