The smallest daily tidal range occurs during which type of tide

It occurs during neap tide

Usually occur on the first or the last quarter of the moon, when the generating forces of the moon and the sun oppose each other.

By opposing each other, their tide-generating forces only produced the smallest rise and fall of the tidal level

I'm pretty sure there's a geometry rule for   anyways, if the triangle is equilateral, and the circle is circumscribed, the circle is outside of the triangle.  to find the area, you need the radius.  the radius should be a straight line from the center of the triangle to any of it's points.  draw lines from the center of the circle to each of the triangle points.  draw three more lines from the center to the middle of the sides of the triangle.  you should now have six separate 30-60-90 triangles inside of your original triangle. use your 30-60-90 rules to solve for the radius, then the circumference. 

Can you give us more information about this question and i will try to you as much as i can