# Chapter 4 - Section 4.5 - Graphs of Sine and Cosine Functions - Exercise Set - Page 597: 76

28 days

#### Work Step by Step

Based on the given graph, the emotional cycle is represented by the blue curve. On 02/01/15, the curve reaches a zero; after one period it will reach zero again on 02/29/15. The number of days in between is $29-1=28$ days, which gives the period.

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