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Question: The angle between lines whose direction ratio are 1, 1, 2 and \(\sqrt{3}\) – 1, \(\sqrt{3}\) – 1, 4 ...

The angle between lines whose direction ratio are 1, 1, 2 and 3\sqrt{3} – 1, 3\sqrt{3} – 1, 4 is

A

450

B

300

C

600

D

900

Answer

600

Explanation

Solution

Apply cos q =a1a2+b1b2+c1c2a12+b12+c12a22+b22+c22\frac{a_{1}a_{2} + b_{1}b_{2} + c_{1}c_{2}}{\sqrt{a_{1}^{2} + b_{1}^{2} + c_{1}^{2}}\sqrt{a_{2}^{2} + b_{2}^{2} + c_{2}^{2}}}

Here a1, b1, c1

̃ 2, –1, 1

a2 , b2, c2 ̃ 1, 1, 2

\ cos q = 2(1)+1(1)+1(2)66=36\frac{2(1) + 1( - 1) + 1(2)}{\sqrt{6}\sqrt{6}} = \frac{3}{6}

cos q = 12=θ=π3\frac{1}{2} = \theta = \frac{\pi}{3}