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TS EAMCET · Maths · Vector Algebra

If the angle between the planes \(\bar{r} \cdot(11 \hat{i}-2 \hat{j}+\alpha \hat{k})=7\) and \(\bar{r} \cdot(2 \hat{i}+4 \hat{j}-2 \hat{k})=5\) is \(\frac{\pi}{2}\), then \(\alpha=\)

  1. A 2
  2. B 3
  3. C 5
  4. D 7
Verified Solution

Answer & Solution

Correct Answer

(D) 7

Step-by-step Solution

Detailed explanation

Given planes are \(\bar{r} \cdot(11 \hat{i}-2 \hat{j}-\alpha \hat{k})=7\) and \(\overline{\mathrm{r}} \cdot(2 \hat{\mathrm{i}}+4 \hat{\mathrm{j}}-2 \hat{\mathrm{k}})=5\) \(\Rightarrow \mathrm{n}_1 \cdot \mathrm{n}_2=0 \Rightarrow 22-8-2 \alpha=0\) or \(\alpha=7\)
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