An equilateral triangle is inscribed in a circle of radius 6r. Express the area A within the circle but outside the triangle as a function of x, if the length of a side of the triangle is 9 x.
The formula for the area is A(x)
A(x) = π(6r)^2 - 3(1/2)(9x)(9x√3/2)
A(x) = 36πr^2 - 81x^2√3
Therefore, the area A within the circle but outside the triangle as a function of x is A(x) = 36πr^2 - 81x^2√3.