Suppose $\langle\mathbf{v}, \mathbf{w}\rangle_1$ and $\langle\mathbf{v}, \mathbf{w}\rangle_2$ are two inner products on the same vector space $V$. For which $\alpha, \beta \in \mathbb{R}$ is the linear combination $\langle\mathbf{v}, \mathbf{w}\rangle=\alpha\langle\mathbf{v}, \mathbf{w}\rangle_1+\beta\langle\mathbf{v}, \mathbf{w}\rangle_2$ a legitimate inner product?