Gujarati
3-1.Vectors
hard

If for two vector $\overrightarrow A $ and $\overrightarrow B $, sum $(\overrightarrow A + \overrightarrow B )$ is perpendicular to the difference $(\overrightarrow A - \overrightarrow B )$. The ratio of their magnitude is

A

$1$

B

$2$

C

$3$

D

None of these

Solution

(a) $(\overrightarrow A + \overrightarrow B )$ is perpendicular to $(\overrightarrow A – \overrightarrow B )$. Thus

$(\overrightarrow A + \overrightarrow B )$.$(\overrightarrow A – \overrightarrow B ) = 0$
or ${A^2} + \overrightarrow B \,.\,\overrightarrow A – \overrightarrow A \,.\,\overrightarrow B – {B^2} = 0\,$
Because of commutative property of dot product

$\overrightarrow A .\overrightarrow B = \overrightarrow B .\overrightarrow A $

$\therefore $${A^2} – {B^2} = 0$ or $A = B$

Thus the ratio of magnitudes $A/B = 1$

Standard 11
Physics

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