Angle between two vectors vec A = 3hat{i} + 4hat{j} + 5hat{k} and vec B = 3hat{i} + 4hat{j} + 5hat{k

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3-1.Vectors

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The angle between the two vectors $\vec A = 3\hat i + 4\hat j + 5\hat k$ and $\vec B = 3\hat i + 4\hat j + 5\hat k$ is ....... $^o$

A

$60$

B

$0$

C

$90$

D

None of these

Solution

(b) $\cos \theta = \frac{{\overrightarrow A .\overrightarrow B }}{{|A||B|}} = \frac{{9 + 16 + 25}}{{\sqrt {9 + 16 + 25} \sqrt {9 + 16 + 25} }}$

$=\frac{{50}}{{50}} = 1\rightarrow \cos \theta = 1$

$\therefore \theta = {\cos ^{ – 1}}(1)$

Standard 11

Physics

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