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Mathematics · 2024 · 3 marks
CBSE 2024 · Region 5 · Set 3 · Q30
Find the projection of vector ( b + c ) on vector a, where a =2 i +2 j + k, b = i +3 j + k and c = i + k.
Find the projection of vector ( $\displaystyle \vec{\mathrm{b}}+\vec{\mathrm{c}}$ ) on vector $\displaystyle \vec{a}$, where $\displaystyle \vec{a}=2 \hat{\mathrm{i}}+2 \hat{\mathrm{j}}+\hat{\mathrm{k}}$, $\displaystyle \overrightarrow{\mathrm{b}}=\hat{\mathrm{i}}+3 \hat{\mathrm{j}}+\hat{\mathrm{k}}$ and $\displaystyle \overrightarrow{\mathrm{c}}=\hat{\mathrm{i}}+\hat{\mathrm{k}}$.
Marking-scheme solution
$$\vec{\mathrm{b}}+\vec{\mathrm{c}}=2 \hat{\mathrm{i}}+3 \hat{\mathrm{j}}+2 \hat{\mathrm{k}}
$$
Projection of $\displaystyle (\vec{\mathrm{b}}+\vec{\mathrm{c}})$ on $\displaystyle \vec{a}=\frac{(\vec{\mathrm{b}}+\vec{\mathrm{c}}) \cdot \vec{a}}{|\vec{a}|}=\frac{4+6+2}{\sqrt{4+4+1}}$
$$=4
$$
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