Chapter 6 - Inverse Functions - 6.7 Hyperbolic Functions - 6.7 Exercises - Page 489: 7

$\sinh(-x) = -\sinh(x)$

Since, we have formula for $\sinh(x) = \dfrac{e^{x} - e^{-x}}{2}$ Thus, $ \sinh(-x) = \dfrac{e^{-x} - e^{-(-x)}}{2}=\dfrac{e^{-x} - e^{-x}}{2}$ or, $= \dfrac{-(e^{x} - e^{-x})}{2}$ or, $= -\sinh(x)$