Chapter 4 - Graphs of the Circular Functions - Section 4.1 Graphs of the Sine and Cosine Functions - 4.1 Exercises - Page 147: 60d

$\Delta S = 0$ when $N = 82.5$

$\Delta S = 0.034~S~sin~[\frac{2\pi~(82.5-N)}{365.25}]$ $\Delta S = 0$ when $sin~[\frac{2\pi~(82.5-N)}{365.25}] = 0$ Then $\frac{2\pi~(82.5-N)}{365.25} = 0$ Then $N = 82.5$ $\Delta S = 0$ when $N = 82.5$