Răspuns:
Explicație pas cu pas:
Notam cu A, B, C, D cele 4 numere.
Avem:
[tex]A=\frac{D+B}{2} \\\\B=\frac{A+C}{2} \\\\C=\frac{B+D}{2} \\\\D=\frac{C+A}{2}[/tex]
[tex]A=\frac{D+B}{2}=\frac{B+D}{2}=C[/tex]
[tex]B=\frac{A+C}{2} =\frac{C+A}{2} = D[/tex]
deci C = A si D = B
[tex]A=\frac{D+B}{2}=\frac{2*D}{2}=D[/tex]
⇒ C = A = D =B
