Question

The sum of two numbers is 20. Find the numbers and their product if their product is a maximum.

Answer 1

x+y=20
C=xy
=x(20-x)
=20x-x^2

if you know calculus,
dC/dx=20-2x=0

x=10 (when maximum)
y=10

if not,

C=-(x-10)^2+100
C becomes maximum when x=10 (-(x-10)^2>0)

x=10 when maximum
y=10

Answer 2

thanks i get it... i'll do it the noncalculus way XD