Question

The projection of \(\vec{b}\) on \(\vec{a}\) is 12. If the angle between \(\vec{a}\) and \(\vec{b}\) is \(60^\circ\), then \(|\vec{b}| =\)

• A. 6
• B. 12
• C. 18
• D. 20
• E. 24

Hint:

Projection is basically the "shadow" of one vector on the other. If the shadow is 12 and the angle is \(60^\circ\), the original length must be twice the shadow length since \(\cos 60^\circ = 0.5\).

Answer 1

Answer: (E)