If α,β,γ are the angles made by a vector with the coordinate axes in the positive direction, then the range of sinαsinβ+sinβsinγ+sinγsinα is
A
[−1,1]
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B
[−12,1]
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C
[−1,2]
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D
[0,1]
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Solution
The correct option is C[−1,2] When α,β and γ are the angles made with co-ordinate axes, we know that
cos2α + cos2β+cos2γ=1
hence sin2α+sin2β+sin2γ=2 Now taking two extreme case, one that sinα=sinβ=sinγ=23 and the second one, sinα=sinβ=−1sinγ=0. Thus the value of sinαsinβ+sinαsinγ+sinβsinγ becomes 2 for the first case and becomes −1 for the second case and thus we get the answer.