question_answer

If \[\Delta \text{ABC}\] is an equilateral triangle of side 'a' and D is a point on BC such that BD = - BC, what is the length of AD?

A)  \[\sqrt{\frac{7}{3}}a\]                  

B)  \[\frac{3}{\sqrt{7}}{{a}^{2}}\]

C)  \[\frac{\sqrt{7}}{3}a\]                  

D)  \[\frac{\sqrt{7}}{3}{{a}^{2}}\]