a)
$A{{F}^{2}}=M{{A}^{2}}-M{{F}^{2}}$
$B{{D}^{2}}=M{{B}^{2}}-M{{D}^{2}}$
$C{{E}^{2}}=M{{C}^{2}}-M{{E}^{2}}$
$\Rightarrow A{{F}^{2}}+B{{D}^{2}}+C{{E}^{2}}=\left( M{{A}^{2}}+M{{B}^{2}}+M{{C}^{2}} \right)-\left( M{{D}^{2}}+M{{E}^{2}}+M{{F}^{2}} \right)$
b)
$A{{E}^{2}}=M{{A}^{2}}-M{{E}^{2}}$
$B{{F}^{2}}=M{{B}^{2}}-M{{F}^{2}}$
$C{{D}^{2}}=M{{C}^{2}}-M{{D}^{2}}$
$\Rightarrow A{{E}^{2}}+B{{F}^{2}}+C{{D}^{2}}=\left( M{{A}^{2}}+M{{B}^{2}}+M{{C}^{2}} \right)-\left( M{{D}^{2}}+M{{E}^{2}}+M{{F}^{2}} \right)$
$\Rightarrow A{{E}^{2}}+B{{F}^{2}}+C{{D}^{2}}=A{{F}^{2}}+B{{D}^{2}}+C{{E}^{2}}$
