E

Use the variance techniques.

B it is

C
Area of the equilateral triangle = (3^(1/2)/4) *a^2 (a is the equilateral side)
--> 9*3^(1/2)=(3^(1/2)/4) *a^2
--> a = 36^(1/2) = 6

Circumscribed circle radius=[3^(1/2)/3]*a= 2*3^(1/2)

Area of the circle = pi*a^2=12pi

chose E

Chose D
To me, A and D are contenders. But "an expense" in A is irrelevant.

A 1. n odd --> n=2k+1 --> n^2-1=(n-1)*(n+1)=(2k+1-1)*(2k+1+1) = 4k(k+1) k(k+1) : 2 (remainder=0) --> 4k(k+1):8 --> sufficient 2. n is not divisible by 8 Ex: n=1 --> n^2-1=(n-1)(n+1)=0 --> divisible by 8 n=2 --> n^2-1 is not divisible by 8 --> insufficient --> A