Tendons are, essentially, elastic cords stretched between two fixed ends; as such, they can support standing waves. These resonances can be undesirable. The Achilles tendon connects the heel with a muscle in the calf. A woman has a 20-cm-long tendon with a cross-section area of 110 mm². The density of tendon tissue is 1100 kg/m³. For a reasonable tension of 500 N, what will be the resonant frequencies of her Achilles tendon?