Chapter 6 - 6.4 - Graphs of Sine and Cosine Functions - 6.4 Exercises - Page 464: 9

$Amplitude=\frac{1}{2}$ $Period=\frac{8\pi}{5}$

If $y=a~sin(bx)$ $Amplitude=|a|$ $Period=\frac{2\pi}{b}$ $y=-\frac{1}{2}~sin(\frac{5x}{4})$ $Amplitude=|-\frac{1}{2}|=\frac{1}{2}$ $Period=\frac{2\pi}{\frac{5}{4}}=2\pi\frac{4}{5}=\frac{8\pi}{5}$