If the vectors a→=iˆ−jˆ+2kˆ,b→=2iˆ+4jˆ+kˆ and c→=λiˆ+jˆ+μkˆ are mutually orthogonal, then (λ,μ)=(2,−3)(−2,3)(3,−2)(−3,2)
Question
If the vectors a→=iˆ−jˆ+2kˆ,b→=2iˆ+4jˆ+kˆ and c→=λiˆ+jˆ+μkˆ are mutually orthogonal, then (λ,μ)=(2,−3)(−2,3)(3,−2)(−3,2)
Solution
The vectors a, b, and c are mutually orthogonal if their dot products are zero. This means that:
a.b = 0 a.c = 0 b.c = 0
Let's calculate these dot products:
- a.b = (iˆ−jˆ+2kˆ).(2iˆ+4jˆ+kˆ) = 21 - 14 + 2*1 = 0
- a.c = (iˆ−jˆ+2kˆ).(λiˆ+jˆ+μkˆ) = λ1 - 11 + 2*μ = 0
- b.c = (2iˆ+4jˆ+kˆ).(λiˆ+jˆ+μkˆ) = 2λ + 41 + μ*1 = 0
From the second equation, we get λ = 1 - 2μ. Substituting this into the third equation, we get:
2*(1 - 2μ) + 4 + μ = 0 2 - 4μ + 4 + μ = 0 -3μ + 6 = 0 μ = 2
Substituting μ = 2 into the equation λ = 1 - 2μ, we get λ = 1 - 2*2 = -3.
So, (λ,μ) = (-3,2), which corresponds to the fourth option.
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