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CBSE Class 12 Mathematics 2026 Main Paper 65/3/3 · Q11 Marksdot_products

CBSE Class 12 Mathematics 2026 Main Paper 65/3/3 · Question 1 (Vector Algebra)

If (a+b)·(a−b)=198 and |a|=10|b|, choose the true statement.

(A) |a|=√2
(B) |b|=√2
(C) |b|=10√2
(D) |a|=10/√2

✅ Step-by-Step Solution

Final Answer: |b|=√2

The mixed terms cancel, leaving |a|²−|b|²=99|b|²=198. Thus |b|=√2.

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