Q46 / 100 · NTA Abhyas (JEE Main) 2020 · Mathematics · Vector Algebra

Given a→, b→ and c→ are 3 vectors such that b→,c→ are parallel unit vectors and a→=3. If a→+λc→=4b→, then the sum of all the possible positive values of λ is

Correct answer: 8

Solution

a→=4b→-λc→
a→|2=16b→2+λ2c→2-8λb→.c→
9=16+λ2-8λb→.c→
⇒λ2-8λ+7=0  as b→⋅c→=1
Sum of all the values of λ=8

Hence, the correct answer is 8.

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