Question Number 174074 by AgniMath last updated on 24/Jul/22
Commented by infinityaction last updated on 24/Jul/22
$${ay}\:=\:{bx}\:,\:{cy}\:={bz}\:,\:{cx}\:=\:{az} \\ $$$$\frac{{ax}−{by}}{\left({a}+{b}\right)\left({x}−{y}\right)}+\frac{{by}−{cz}}{\left({b}+{c}\right)\left({y}−{z}\right)}+\frac{{cz}−{ax}}{\left({c}+{a}\right)\left({z}−{x}\right)}\: \\ $$$$\frac{{ax}−{by}}{\left({a}+{b}\right)\left({x}−{y}\right)}−\mathrm{1}+\frac{{by}−{cz}}{\left({b}+{c}\right)\left({y}−{z}\right)}−\mathrm{1}+\frac{{cz}−{ax}}{\left({c}+{a}\right)\left({z}−{x}\right)}−\mathrm{1}+\mathrm{3} \\ $$$$\frac{{ay}−{bx}}{\left({a}+{b}\right)\left({x}−{y}\right)}+\frac{{bz}−{cy}}{\left({b}+{c}\right)\left({y}−{z}\right)}+\frac{{cx}−{az}}{\left({c}+{a}\right)\left({z}−{x}\right)}+\mathrm{3} \\ $$$$\:\mathrm{0}+\mathrm{0}+\mathrm{0}+\mathrm{3}\:=\:\mathrm{3}\:\:\:\:\:\:\:\:\:\:\: \\ $$
Answered by som(math1967) last updated on 24/Jul/22
$${let}\:\frac{{x}}{{a}}=\frac{{y}}{{b}}=\frac{{z}}{{c}}={k}\:\:\left[{k}\neq\mathrm{0}\right] \\ $$$$\Rightarrow{x}={ak},{y}={bk}\:,{z}={ck} \\ $$$$\frac{{k}\left({a}^{\mathrm{2}} −{b}^{\mathrm{2}} \right)}{{k}\left({a}+{b}\right)\left({a}−{b}\right)}\:+\frac{{k}\left({b}^{\mathrm{2}} −{c}^{\mathrm{2}} \right)}{{k}\left({b}+{c}\right)\left({b}−{c}\right)} \\ $$$$\:\:\:\:\:\:\:\:\:\:+\frac{{k}\left({c}^{\mathrm{2}} −{a}^{\mathrm{2}} \right)}{{k}\left({c}+{a}\right)\left({c}−{a}\right)} \\ $$$$=\frac{\left({a}^{\mathrm{2}} −{b}^{\mathrm{2}} \right)}{\left({a}^{\mathrm{2}} −{b}^{\mathrm{2}} \right)}\:+\frac{\left({b}^{\mathrm{2}} −{c}^{\mathrm{2}} \right)}{\left({b}^{\mathrm{2}} −{c}^{\mathrm{2}} \right)}\:+\frac{\left({c}^{\mathrm{2}} −{a}^{\mathrm{2}} \right)}{\left({c}^{\mathrm{2}} −{a}^{\mathrm{2}} \right)} \\ $$$$=\mathrm{1}+\mathrm{1}+\mathrm{1}=\mathrm{3} \\ $$