The sides of a parallelogram are $2\hat{i}+4\hat{j}-5\hat{k}$ and $\hat{i}+2\hat{j}+3\hat{k}$ . The unit vector parallel to one of the diagonals is a. $\frac{1}{7}\left(3\hat{i}+6\hat{j}-2\hat{k}\right)$ b. $\frac{1}{7}\left(3\hat{i}-6\hat{j}-2\hat{k}\right)$ c. $\frac{1}{\sqrt{69}}\left(\hat{i}+6\hat{j}+8\hat{k}\right)$ d. $\frac{1}{\sqrt{69}}\left(-\hat{i}-2\hat{j}+8\hat{k}\right)$

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