In $\triangle ABC$ with sides $a, b, c$ opposite to vertices $A, B, C$ and medians $d, e, f$ from $A, B, C$ respectively, $d^2 =$

• a$\dfrac{2(b^2+c^2) - a^2}{4}$
• b$\dfrac{2(a^2+c^2) - b^2}{4}$
• c$\dfrac{2(a^2+b^2) - c^2}{4}$
• d$\dfrac{a^2+b^2+c^2}{4}$