A guitar string has a tension T, length L, and diameter D. Give the multiplicative factor by which the fundamental frequency of the string changes under the following conditions: (a) The tension in the string is increased by a factor of 4. The diameter is D and the lenght is L. (b) The diameter of the string is increased by a factor of 3. The tension is T and the length is L. (c) The length of the string is halved. The tension is T and the diameter is D.