z=x²-xy+y²+9x-6y+20
∂z/∂x=2x-y+9
∂z/∂y=-x+2y-6
2x-y+9=0
-x+2y-6=0
2x-y+9=0
3y-3=0 => y=1, x=-4
∂²z/∂x²=2=A
∂²z/∂x∂y=0=B
∂²z/∂y²=2=C
Δ=AC-B²=4 > 0, A > 0
Zmin(-4;1)=16+4+1-36-6+20=-1
2 = 14/7, 22/11
4 = 28/7, 44/11
5 = 35/7, 55/11
27 = 189/7, 297/11
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
1)2800:4·1=700(л)
2)2800+700=3500(л)
3)3500:25=140(б.)
Оьвет:140 бидонов понадобится.