Bonjour,

M = (a+b)/c + (a+c)/b + (b+c)/a

= [ab(a+b) + ac(a+c) + bc(b+c)]/abc

= [a²b + ab² + a²c + ac² + b²c + bc²]/abc

= [(ab + ac + bc)(a + b + c) - 3abc]/abc

= -3abc/abc

= -3