BITSAT 2017 Paper

Since the equilateral triangle is inscribed in the circle with centre at the origin, centroid lies on the origin.
So,

AO

OD

=

2

1

⇒OD=‌‌

1

2

AO=‌‌

a

2

So, other vertices of triangle have coordinates,
(−‌‌

a

2

,‌‌

√3a

2

) and‌[−‌‌

a

2

,−‌‌

√3

2

a]
(−‌‌

a

2

,‌‌

√3

2

a)(−‌‌

a

2

,‌‌

√3

2

a)
∴ Equation of line BC is
x=−

a

2

⇒2x+a=0