Question Number 75849 by behi83417@gmail.com last updated on 18/Dec/19
$$\boldsymbol{\mathrm{In}}\:\boldsymbol{\mathrm{a}}\:\boldsymbol{\mathrm{A}}\overset{\bigtriangleup} {\boldsymbol{\mathrm{B}C}}: \\ $$$$\begin{cases}{\boldsymbol{\mathrm{a}}+\boldsymbol{\mathrm{b}}+\boldsymbol{\mathrm{c}}=\mathrm{2}\left(\boldsymbol{\mathrm{h}}_{\boldsymbol{\mathrm{a}}} +\boldsymbol{\mathrm{h}}_{\boldsymbol{\mathrm{b}}} +\boldsymbol{\mathrm{h}}_{\boldsymbol{\mathrm{c}}} \right)}\\{\boldsymbol{\mathrm{a}}^{\mathrm{2}} +\boldsymbol{\mathrm{b}}^{\mathrm{2}} +\boldsymbol{\mathrm{c}}^{\mathrm{2}} =\mathrm{6}\boldsymbol{\mathrm{abc}}}\\{\boldsymbol{\mathrm{h}}_{\boldsymbol{\mathrm{a}}} ^{\mathrm{2}} +\boldsymbol{\mathrm{h}}_{\boldsymbol{\mathrm{b}}} ^{\mathrm{2}} +\boldsymbol{\mathrm{h}}_{\boldsymbol{\mathrm{c}}} ^{\mathrm{2}} =\mathrm{6}\boldsymbol{\mathrm{h}}_{\boldsymbol{\mathrm{a}}} .\boldsymbol{\mathrm{h}}_{\boldsymbol{\mathrm{b}}} .\boldsymbol{\mathrm{h}}_{\boldsymbol{\mathrm{c}}} }\end{cases} \\ $$$$\boldsymbol{\mathrm{find}}:\measuredangle\boldsymbol{\mathrm{A}} \\ $$