ghadi ntal9ou (commencer) mn 1+cos(x)=2cos²(x/2) et nada3ou x=pi/2^n et nou3awido pi/2^n fi 1+c....... fa najidou 1+cos(pi/2^n)=2cos²(pi/2^n+1) et nadribou tarafayn f 2 et nada3ou ljadr (cosx>0) najidou v2+2cos(pi/2^n)=2cos(pi/2^n+1) noula7idou ana v2+2cos(pi/2^n)=A(n) wa bitali A(n)=2cos(pi/2^(n+1))