Answer: the three positive numbers are; 70, 70, 70
Step-by-step explanation:
Given that sum is equal = 210
Lets ( x, y, z ) be the three positive numbers
such that
x + y + z = 210
what is the maximum of xyz
take f(x,y,z) = xyz
Q(x,y,z) = 0
x + y + z -210 = 0
consider the function
F(x,y,z) = f(x,y,z) + λQ(x,y,z)
F = xyz + λ(x+y+z-210)
dF/dx = 0 ⇒ yz + λ(1) = 0 ⇒ λ = -yz ..............equ(1)
dF/dy = 0 ⇒ xz + λ(1) = 0 ⇒ λ = -xz.................equ(2)
dF/dz = 0 ⇒ xy + λ(1) = 0 ⇒ λ = -xy...............equ(3)
Now
equ(1)/equ(2) ⇒ λ/λ = -yz/-xz ⇒ x = +y
equ(1)/equ(3) ⇒ λ/λ = - yz/-xy ⇒ x = +z
⇒ y = z = x
by substitution
x + y + z = 210
x + x + x = 210
3x = 210
x = 210/3 = 70
∴ x, y, z = 70, 70 ,70
MAXIMUM
∛xyz = 70 { when x = y = z = 70}
