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Mathematics · 2026 · 1 mark
CBSE 2026 · Region 3 · Set 1 · Q15
If ( a + b ) ·( a - b )=198 and | a |=10| b |, then:
If $\displaystyle (\vec{\mathrm{a}}+\vec{\mathrm{b}}) \cdot(\vec{\mathrm{a}}-\vec{\mathrm{b}})=198$ and $\displaystyle |\vec{\mathrm{a}}|=10|\vec{\mathrm{b}}|$, then :
Official answer
(B)
$\displaystyle |\overrightarrow{\mathrm{b}}|=\sqrt{2}$
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