The triangle inequality for vectors states:
A$|\vec a + \vec b| = |\vec a| + |\vec b|$
B$|\vec a + \vec b| \le |\vec a| + |\vec b|$
C$|\vec a + \vec b| \ge |\vec a| + |\vec b|$
D$|\vec a + \vec b| = |\vec a| - |\vec b|$
Answer & Solution
Correct answer: B. $|\vec a + \vec b| \le |\vec a| + |\vec b|$
In any triangle, the third side cannot exceed the sum of the other two: $|\vec a + \vec b| \le |\vec a| + |\vec b|$, with equality only when $\vec a$ and $\vec b$ are parallel and same-direction.
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