Inside a particular isosceles triangle there are four congruent unit circles (radius=1) tangent along its base. The circles on the end are also tangent to the lateral sides of the triangle.

Then a circle of radius R is tangent to the two middle unit circles and the two lateral sides of the triangle.

Finally one more unit circle is placed atop the larger circle tangent to it and the two lateral sides.

What is the radius of the large circle?

Can you generalize for N circles along the base?

For comparison, the classic problem Four Tangent Circles is a version of this one with only two unit circles at the base.