Direction Cosines and Direction Ratios — Maths STD 12 Science — Question
Gujarat BoardEnglish MediumSTD 12 ScienceMathsDirection Cosines and Direction Ratios3 Marks
Question
Write the angle between the lines whose direction ratios are perportional to 1, -2, 1 and 4, 3, 2.
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Answer
The direction ratios of the first line are 1, -2, 1 and the direction ratios of the second line are 4, 3, 2.
Let $\theta$ be the angle between these two lines.
Now,
$\cos\theta =\Bigg|\frac{1(4)+(-2)(3)+1(2)}{\sqrt{(1)^2+(-2)^2+(1)^2}\sqrt{(4)^2+(3)^2+(2)^2}}\Bigg|$
$=\Bigg|\frac{4+6+2}{\sqrt{1+4+1}\sqrt{16+9+4}}\Bigg|$
$=\frac{0}{\sqrt{6}\sqrt{29}}$
$=0$
$\Rightarrow\theta=\frac{\pi}{2}$
Hence, the required angle is$\frac{\pi}{2}$.
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