question_answer

If r be position vector of any point on a sphere and a, b are respectively position vectors of the extremities of a diameter, then [MP PET 1994]

A)            \[\mathbf{r}\,.\,(\mathbf{a}-\mathbf{b})=0\]

B)            \[\mathbf{r}\,.\,(\mathbf{r}-\mathbf{a})=0\]

C)            \[(\mathbf{r}+\mathbf{a})\,.\,(\mathbf{r}+\mathbf{b})=0\]

D)            \[(\mathbf{r}-\mathbf{a})\,.\,(\mathbf{r}-\mathbf{b})=0\]