Summer Problem Solving Marathon Solution #5

We have d = ⁴⁄_c. c = πd, so by substitution d = ⁴⁄_πd. Cross-multiplying, πd²=4, and d²=⁴⁄_π.

Since r = ^d⁄₂, r² = ^d2⁄₄. So the area of the circle is πr² = π(^d2⁄₄) = π(¹⁄_π) = 1.