The angle $\theta$ between two planes with normal vectors $\vec{n}_1$ and $\vec{n}_2$ satisfies
- $\cos\theta=\dfrac{\vec{n}_1\cdot\vec{n}_2}{|\vec{n}_1||\vec{n}_2|}$
- $\cos\theta=\dfrac{\vec{n}_1\times\vec{n}_2}{|\vec{n}_1||\vec{n}_2|}$
- $\sin\theta=\dfrac{\vec{n}_1\cdot\vec{n}_2}{|\vec{n}_1||\vec{n}_2|}$
- $\tan\theta=\dfrac{\vec{n}_1\cdot\vec{n}_2}{|\vec{n}_1||\vec{n}_2|}$
Show answer and solution
Correct answer: A. $\cos\theta=\dfrac{\vec{n}_1\cdot\vec{n}_2}{|\vec{n}_1||\vec{n}_2|}$
The angle between two planes is equal to the angle between their normal vectors.
**Therefore $\cos\theta=\dfrac{\vec{n}_1\cdot\vec{n}_2}{|\vec{n}_1||\vec{n}_2|}$.**