Answer:
The two numbers are:
x = 500
y = 125
Step-by-step explanation:
We want to find two numbers x and y, such that:
x + 4*y = 1000
f(x, y) = x*y is maximum.
From the first equation, we can isolate one of the variables to get
x = 1000 - 4y
now we can replace it in f(x, y):
x*y = (1000 - 4*y)*y = 1000*y - 4*y^2
So now we want to maximize the function:
f(y) =- 4*y^2 + 1000*y
where y must be an integer.
Notice that this is a quadratic equation with a negative leading coefficient (so the arms of the graph will open downwards), thus, the maximum will be at the vertex.
Remember that for a general quadratic equation:
y = a*x^2 + bx + c
the x-value of the vertex is:
x = -b/(2*a)
so, in the case of:
f(y) =- 4*y^2 + 1000*y
the y-value of the vertex will be:
y = -1000/(2*-4) = 1000/8 = 125
So we found the value of y.
now we can use the equation:
x = 1000 - 4*y
x = 1000 - 4*125 = 1000 - 500 = 500
x = 500
Then the two numbers are:
x =500
y = 125
when r=8.
