If →a=→b+→c, then is it true that |→a|=|→b|+|→c|? Justify your answer.
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Solution
In ΔABC, let →CB=→a,→CA=→b, and
→AB=→c (as shown in the following figure). Now, by the triangle law of vector addition, we have →a=→b+→c. It is clearly known that |→a|,|→b|, and |→c| represent the sides of ΔABC. Also, it is known that the sum of the lengths of any two sides of a triangle is greater than the third side. ∴|→a|<|→b|+|→c| Hence, it is not true that |→a|=|→b|+|→c|.