Verified Solution • 2025–26 Session moderate

QJEEM25Ma74b7: JEE Main 2025 Physics - Class 11 JEEM25Ma74b7 Solution: If the components of along and perpendicular to respectively,…

If the components of a⃗=αi^+βj^+γk^\vec{a}=\alpha \hat{i}+\beta \hat{j}+\gamma \hat{k} along and perpendicular to b⃗=3i^+j^−k^\vec{b}=3 \hat{i}+\hat{j}-\hat{k} respectively, are 1611(3i^+j^−k^)\frac{16}{11}(3 \hat{i}+\hat{j}-\hat{k}) and 111(−4i^−5j^−17k^)\frac{1}{11}(-4 \hat{i}-5 \hat{j}-17 \hat{k}) , then α2+β2+γ2\alpha^2+\beta^2+\gamma^2 is equal to :

Multiple Choice Options

  • A 16
  • B 23
  • C 26
  • D 18

Step-by-Step Verified Solution

amp; let amp;a→11= component of a→ along b→amp;a→1= component of a→ perpendicular to b→amp;a→11=1611(3i^+j^−k^)amp;a→1=111(−4i^−5j^−17k^)amp;∵a→=a→11+a→1amp;∴a→=1611(3i^+j^−k^)+111(−4i^−5j^−17k^)amp;=4411i^+1111j^−3311k^amp;a→=4i^+j^−3k^amp;α=4β=1γ=−3α2+β2+γ2=16+1+9=26\begin{aligned}& \text { let } \\& \overrightarrow{\mathrm{a}}_{11}=\text { component of } \overrightarrow{\mathrm{a}} \text { along } \overrightarrow{\mathrm{b}} \\& \overrightarrow{\mathrm{a}}_1=\text { component of } \overrightarrow{\mathrm{a}} \text { perpendicular to } \overrightarrow{\mathrm{b}} \\& \overrightarrow{\mathrm{a}}_{11}=\frac{16}{11}(3 \hat{\mathrm{i}}+\hat{\mathrm{j}}-\hat{\mathrm{k}}) \\& \overrightarrow{\mathrm{a}}_1=\frac{1}{11}(-4 \hat{\mathrm{i}}-5 \hat{\mathrm{j}}-17 \hat{\mathrm{k}}) \\& \because \overrightarrow{\mathrm{a}}=\overrightarrow{\mathrm{a}}_{11}+\overrightarrow{\mathrm{a}}_1 \\& \therefore \overrightarrow{\mathrm{a}}=\frac{16}{11}(3 \hat{\mathrm{i}}+\hat{\mathrm{j}}-\hat{\mathrm{k}})+\frac{1}{11}(-4 \hat{\mathrm{i}}-5 \hat{\mathrm{j}}-17 \hat{\mathrm{k}}) \\& \quad=\frac{44}{11} \hat{\mathrm{i}}+\frac{11}{11} \hat{\mathrm{j}}-\frac{33}{11} \hat{\mathrm{k}} \\& \overrightarrow{\mathrm{a}}=4 \hat{\mathrm{i}}+\hat{\mathrm{j}}-3 \hat{\mathrm{k}} \quad \\& \begin{array}{l}\alpha=4 \qquad \beta=1\qquad \gamma=-3\\\alpha^2+\beta^2+\gamma^2=16+1+9=26\end{array}\end{aligned}

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