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AP EAMCET · Maths · Three Dimensional Geometry

If the direction cosines of a line are \(\left(\frac{a}{\sqrt{83}}, \frac{5}{\sqrt{83}}, \frac{c}{\sqrt{83}}\right)\) and \(c-a=4\), then \(c a=\)

  1. A \(24\)
  2. B \(21\)
  3. C \(18\)
  4. D \(33\)
Verified Solution

Answer & Solution

Correct Answer

(B) \(21\)

Step-by-step Solution

Detailed explanation

Direction cosine of \(a \hat{i}+b \hat{j}+c \hat{k}\) can be \(\frac{a}{\sqrt{a^2+b^2+c^2}}, \frac{b}{\sqrt{a^2+b^2+c^2}}, \frac{c}{\sqrt{a^2+b^2+c^2}}\) According to question, \(\sqrt{a^2+b^2+c^2}=\sqrt{83}, b=5\) \(\Rightarrow \quad a^2+(5)^2+c^2=83\)…