Which of the given set of planes are perpendicular to each other?

[answerhappygod]

a) \(\vec{r}.(2\hat{i}+2\hat{j}+\hat{k})\)=5 and \(\vec{r}.(\hat{i}+2\hat{j}+2\hat{k})\)=5
b) \(\vec{r}.(\hat{i}-2\hat{j}+\hat{k})\)=7 and \(\vec{r}.(\hat{i}+\hat{j}+2\hat{k})\)=2
c) \(\vec{r}.(2\hat{i}-2\hat{j}+\hat{k})\)=4 and \(\vec{r}.(\hat{i}+2\hat{j}+2\hat{k})\)=5
d) \(\vec{r}.(3\hat{i}-2\hat{j}+\hat{k})\)=2 and \(\vec{r}.(\hat{i}+2\hat{j}+8\hat{k})\)=8