Question

What can be the angle between $\vec{P}+\vec{Q}$ and $\vec{P}-\vec{Q}$ ?

• A. $0^{\circ}$
• B. $90^{\circ}$
• C. $180^{\circ}$
• D. between $0^{\circ}$ and $180^{\circ}$

Answer 1

Answer: (D)

between $0^{\circ}$ and $180^{\circ}$

Answer 2

$\vec{P}+\vec{Q}$ and $\vec{P}-\vec{Q}$ are diagonals of a parallelogram whose sides are $\vec{P}$ and $\vec{Q}$ . Thus the angle between them may be between$0^{\circ}$ and $180^{\circ}$