- #1

- 138

- 0

I found one difficult equation for me...

It is:

Valid for real numbers a, b, c, d:

a + b = c + d

ad = bc

ac + bd = 1

What is the maximum of a+b+c+d?

And DON'T SAY wolfram, really no wolfram... I used it and it isn't good.

So... have you got any idea?