Question

Find two numbers whose sum is 42 and whose product will be at the largest possible.

Answer 1

x + y = 42
y = 42-x

x(42-x)
42x-x^2

derivative 42 -2x =0
x=21 y =21

Answer 2

Find two numbers whose sum is 42 and whose product will be at the largest possible.

Answer 3

When the sum of two numbers is constant, then product of those two numbers is maximum, when those two numbers are as close to each other. As 21 + 21 = 42, so answer will be 21 × 21 = 441.