Which from the following is true? (A) $\cos \theta=\left[\left(\left|\mathrm{A}^{\rightarrow} \times \mathrm{B}^{\rightarrow}\right|\right) / \mathrm{AB}\right]$ (B) $\sin \theta=\left[\left(\mathrm{A}^{\rightarrow} \cdot \mathrm{B}^{\rightarrow}\right) / \mathrm{AB}\right]$ (C) $\tan \theta=\left[\left(\left|\mathrm{A}^{\rightarrow} \times \mathrm{B}^{\rightarrow}\right|\right) /\left(\mathrm{A}^{-}-\mathrm{B}^{-}\right)\right]$ (D) $\cot \theta=\left[\mathrm{AB} /\left(\left|\mathrm{A}^{\rightarrow} \times \mathrm{B}^{\rightarrow}\right|\right)\right]$

Short Answer

Expert verified
(D) \(\cot \theta=\frac{\mathrm{AB}}{\left|\mathrm{A}^{\rightarrow} \times \mathrm{B}^{\rightarrow}\right|}\)

Step by step solution

01

Recall the dot product formula and the cosine relationship

The dot product A⃗.B⃗ of two vectors can be represented as \(|\mathrm{A}^{\rightarrow}| |\mathrm{B}^{\rightarrow}| \cos \theta\), where θ is the angle between A⃗ and B⃗. Rearranging the formula, we get \(\cos \theta = \frac{\mathrm{A}^{\rightarrow} \cdot \mathrm{B}^{\rightarrow}}{|\mathrm{A}^{\rightarrow}||\mathrm{B}^{\rightarrow}|}\).
02

Recall the cross product formula and the sine relationship

The cross product |\(A⃗ \times B⃗\)| can be represented as \( |\mathrm{A}^{\rightarrow}||\mathrm{B}^{\rightarrow}| \sin \theta\), where θ is the angle between A⃗ and B⃗. Rearranging the formula, we get \(\sin \theta = \frac{|\mathrm{A}^{\rightarrow} \times \mathrm{B}^{\rightarrow}|}{|\mathrm{A}^{\rightarrow}||\mathrm{B}^{\rightarrow}|}\).
03

Check each statement for correctness

(A) The statement is incorrect because it confuses the cross product and cosine relationship. The correct equation for cosine is: \(\cos \theta = \frac{\mathrm{A}^{\rightarrow} \cdot \mathrm{B}^{\rightarrow}}{|\mathrm{A}^{\rightarrow}||\mathrm{B}^{\rightarrow}|}\). (B) The statement is incorrect because it confuses the dot product and sine relationship. The correct equation for sine is: \(\sin \theta = \frac{|\mathrm{A}^{\rightarrow} \times \mathrm{B}^{\rightarrow}|}{|\mathrm{A}^{\rightarrow}||\mathrm{B}^{\rightarrow}|}\). (C) The statement is incorrect because the denominator is not part of the tangent relationship and does not include any valid vector operations. (D) The statement is correct. Recalling the sine relationship from earlier, we have \(\sin \theta = \frac{|\mathrm{A}^{\rightarrow} \times \mathrm{B}^{\rightarrow}|}{|\mathrm{A}^{\rightarrow}||\mathrm{B}^{\rightarrow}|}\). Inversely, \(\csc \theta = \frac{|\mathrm{A}^{\rightarrow}||\mathrm{B}^{\rightarrow}|}{|\mathrm{A}^{\rightarrow} \times \mathrm{B}^{\rightarrow}|}\). The cotangent function is the reciprocal of the tangent function, and since \(\cot \theta = \frac{ \cos \theta}{\sin \theta}\) and \(\csc \theta = \frac{1}{\sin \theta}\), we can find that \(\cot \theta=\frac{\mathrm{AB}}{\left|\mathrm{A}^{\rightarrow} \times \mathrm{B}^{\rightarrow}\right|}\), which matches the given statement D.

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