θ
0.8π
a
\color{#FF00FF}\mathbf{a}
a
v
\color{#006400}\mathbf{v}
v
v
∥
\color{#9ACD32}\mathbf{v}_{\parallel}
v
∥
v
⊥
\color{#FF1932}\mathbf{v}_{\perp}
v
⊥
v
⊥
′
\color{#FFD700}\mathbf{v}_{\perp}'
v
⊥
′
a
×
v
\color{#00BFFF}\mathbf{a}\times\mathbf{v}
a
×
v
v
′
\color{#FF8C00}\mathbf{v}'
v
′