SOLUTION: Find two numbers differing by 48 whose product is as small as possible.

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Question 1180887: Find two numbers differing by 48 whose product is as small as possible.
Found 2 solutions by ikleyn, MathLover1:
Answer by ikleyn(52903) About Me  (Show Source):
You can put this solution on YOUR website!
.

If x is the smaller number, the the greater number is (x+48), according to the condition,

and the product of the two numbers is  x*(x+48) = x^2 + 48.


They want you find the MINIMUM of this quadratic function.


The minimum is the vertex of the parabola, and on x-axis, this minimum is located
exactly half way between the zeroes of this quadratic function.


The zeroes are -48 and 0, so  x%5Bmin%5D = %28-48+%2B+0%29%2F2 = -24.


The minimal value of the function is  y = (-24)*(-24+48) = (-24)*24 = -576.


ANSWER.  The minimum value of the producr of such two numbers is -576.

         It is achieved at the pair of the numbers (-24,24).



                    Visual check


    


     Plot y = x*(x+48) (red line),  y = -576 (green line)


Solved.



Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

let two numbers be x and y
if they differing by 48+ we have
y=x%2B48..........eq.1
Their product is
P=xy+.......eq.2, substitute x
Since y=x%2B48,
P=%28x%2B48%29x
P=x%5E2%2B48x
minimize the function by calculating P'%28x%29
P'%28x%29=2x%2B48
Setting it to 0, we get
0=2x%2B48
0=2%28x%2B24%29
=>x=-24
then
y=-24%2B48..........eq.1
y=24
so, your numbers are 24 and -24