[m]BM^2=\frac{2AB^2+2BC^2-AC^2}{4}[/m]
⇒ [m](\frac{131}{2})^2=\frac{2\cdot 68^2+2\cdot 87^2-AC^2}{4}[/m]
[m]AC^2=2\cdot 68^2+2\cdot 87^2-131^2[/m]
[m]AC^2=9248+15138-17161=7225=85^2[/m]
AC=85
Тогда
[m]CL^2=\frac{2AC^2+2BC^2-AB^2}{4}[/m]
[m]CL^2=\frac{2\cdot 85^2+2\cdot 87^2-68^2}{4}[/m]
[m]CL^2=\frac{2\cdot 7225+15138-9248}{4}=5085[/m]
[m]CL=\sqrt{5085}[/m]