Question:
If $\vec{a}=(\hat{\mathrm{i}}-\hat{\mathrm{j}}+7 \hat{\mathrm{k}})$ and $\overrightarrow{\mathrm{b}}=(5 \hat{\mathrm{i}}-\hat{\mathrm{j}}+\lambda \hat{\mathrm{k}})$ then find the value of $\lambda$ so that $(\overrightarrow{\mathrm{a}}+\overrightarrow{\mathrm{b}})$ and $(\overrightarrow{\mathrm{a}}-\overrightarrow{\mathrm{b}})$ are orthogonal vectors.
Solution:
