\(\dfrac{b+c}{bc}=\dfrac{2}{a}< =>\dfrac{1}{b}+\dfrac{1}{c}=\dfrac{2}{a}\)
\(< =>\dfrac{1}{b}-\dfrac{1}{a}+\dfrac{1}{c}-\dfrac{1}{a}=0\)
\(< =>\dfrac{a-b}{ab}+\dfrac{a-c}{ac}=0\)
\(< =>\dfrac{a-b}{ab}=\dfrac{a-c}{ac}\)
\(< =>\dfrac{ab}{ac}=\dfrac{a-b}{c-a}< =>\dfrac{b}{c}=\dfrac{a-b}{c-a}\)