MCQ
The direction cosines of the vector $3i - 4j + 5k$ are
  • A
    $\frac{3}{5},\,\frac{{ - 4}}{5},\frac{1}{5}$
  • $\frac{3}{{5\sqrt 2 }},\,\frac{{ - 4}}{{5\sqrt 2 }},\frac{1}{{\sqrt 2 }}$
  • C
    $\frac{3}{{\sqrt 2 }},\,\frac{{ - 4}}{{\sqrt 2 }},\,\frac{1}{{\sqrt 2 }}$
  • D
    $\frac{3}{{5\sqrt 2 }},\,\,\frac{4}{{5\sqrt 2 }},\,\frac{1}{{\sqrt 2 }}$

Answer

Correct option: B.
$\frac{3}{{5\sqrt 2 }},\,\frac{{ - 4}}{{5\sqrt 2 }},\frac{1}{{\sqrt 2 }}$
b
(b) Vector$\overrightarrow A  = 3i - 4j + 5k$ We know that direction cosines of  $\overrightarrow A $

$ = \frac{3}{{\sqrt {{3^2} + {4^2} + {5^2}} }},\,\frac{{ - 4}}{{\sqrt {{3^2} + {4^2} + {5^2}} }},\,\frac{5}{{\sqrt {{3^2} + {4^2} + {5^2}} }}$

$ = \frac{3}{{5\sqrt 2 }},\,\frac{{ - 4}}{{5\sqrt 2 }},\,\frac{1}{{\sqrt 2 }}$.

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