Answer:
The angle between them is 60 degrees
Step-by-step explanation:
Given
[tex]a = 2i + j -3k[/tex]
[tex]b = 3i - 2j -k[/tex]
Required
The angle between them
The cosine of the angle between them is:
[tex]\cos(\theta) = \frac{a\cdot b}{|a|\cdot |b|}[/tex]
First, calculate a.b
[tex]a \cdot b =(2i + j -3k) \cdot (3i - 2j -k)[/tex]
Multiply the coefficients of like terms
[tex]a \cdot b =2 * 3 - 1 * 2 - 3 * -1[/tex]
[tex]a \cdot b =7[/tex]
Next, calculate |a| and |b|
[tex]|a| = \sqrt{2^2 + 1^2 + (-3)^2[/tex]
[tex]|a| = \sqrt{14[/tex]
[tex]|b| = \sqrt{3^2 + (-2)^2 + (-1)^2}[/tex]
[tex]|b| = \sqrt{14}[/tex]
Recall that:
[tex]\cos(\theta) = \frac{a\cdot b}{|a|\cdot |b|}[/tex]
This gives:
[tex]\cos(\theta) = \frac{7}{\sqrt{14} * \sqrt{14}}[/tex]
[tex]\cos(\theta) = \frac{7}{14}[/tex]
[tex]\cos(\theta) = 0.5[/tex]
Take arccos of both sides
[tex]\theta =\cos^{-1}(0.5)[/tex]
[tex]\theta =60^o[/tex]
