question_answer

The centre of the sphere \[\alpha \,\mathbf{r}-2\mathbf{u}.\mathbf{r}=\beta ,(\alpha \ne 0)\] is [AMU 1999]

A)            \[-\mathbf{u}/\alpha \]

B)            \[\mathbf{u}/\alpha \]

C)            \[\alpha \mathbf{u}/\beta \]

D)            \[\frac{\alpha +\beta }{\alpha }\mathbf{u}\]