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Home  >>  JEEMAIN and AIPMT  >>  Mathematics  >>  Class12  >>  Vector Algebra
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The vector that makes equal angle with $\large\frac{1}{3}$$(\hat i-2\hat j+2\hat k), \:\large\frac{1}{5}$$(-4\hat i-3\hat k)$ and $\hat j$ is ?

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  • Angle $\theta$ between $\overrightarrow a\:and\:\overrightarrow b$ is given by $cos\theta=\large\frac{\overrightarrow a.\overrightarrow b}{|\overrightarrow a||\overrightarrow b|}$
Let $\overrightarrow a=\large\frac{1}{3}$$(\hat i-2\hat j+2\hat k),\:\overrightarrow b=\large\frac{1}{5}$$(-4i-3\hat k)$
$\Rightarrow\:|\overrightarrow a|=|\overrightarrow b|=1$
Let $\overrightarrow r=x\hat i+y\hat j+z\hat k$ make equal angle with $\overrightarrow a,\overrightarrow b\:and\:\hat j$
$\Rightarrow \overrightarrow r.\overrightarrow a=\overrightarrow r.\overrightarrow b=\overrightarrow r.\hat j$
solving these three equations we get one of the values
$\therefore\:$The required vector $ = 5\hat i-\hat j-5\hat k$
answered Nov 8, 2013 by rvidyagovindarajan_1

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