Chapter 5 - Inner Product Spaces - 5.2 Inner Product Spaces - 5.2 Exercises - Page 247: 91

see the details.

Using the properties mentioned in the definition of the inner product, \begin{aligned} \langle u+v, w\rangle &=\langle w,u+v\rangle \\ &= \langle w,u\rangle+\langle w,v\rangle\\ &= \langle u,w\rangle+\langle v,w\rangle. \end{aligned}.