From the center of the small circle on the bottom left draw a radius to the tangent formed by the side of the equilateral triangle and draw a segment to the bottom left vertex of the equilateral triangle....call this x
This will form a 30-60-90 right triangle
The vertex angle of the equilateral triangle will be bisected = 30°
The side opposite of this = radius of a small circle = 1
So....x = twice the radius = 2
So.....the distance from the bottom left vertex to the center of the middle circle = x + 2 = 2 + 2 = 4
And we can form another triangle with two sides of 4 and an included angle of 120°
And the side of the equilateral triangle ,S, wil be opposite this angle
So.....using the Law of Cosines
S^2 = 4^2 + 4^2 - 2 (16) cos (120°)
S^2 = 32 - 32 (-1/2)
S^2 = 48
S = sqrt (48)
So....the area of the equilateral triangle =
(1/2) (sqrt (48))^2 sin (60°) =
(1/2) (48) sqrt (3) /2 =
12 sqrt (3) units ^2