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If a vector 2î+3ĵ+8k̂ is perpendicular to the vector 4ĵ-4î+αk̂, then the value of α is

Asked in NEET 2005 · Scalar product and projections

• (1) 1/2
• (2) -1/2
• (3) 1
• (4) -1

Step-by-step solution

Why the other options are wrong

• (1) Drops the minus sign when solving 4+8α=0. The first two terms give +4, so α must be negative to cancel it.
• (3) Comes from reading the k̂ coefficient as 4 rather than 8, giving 4+4α=0 and hence α=-1; and then dropping the sign.
• (4) Comes from the same coefficient slip, 4+4α=0, with the sign kept; the k̂ coefficient of the first vector is 8.

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