If →p and →s are not perpendicular to each other and →r×→p=→q×→p and →r⋅→s=0, then →r is equal to
A
→q+(→q⋅→p→p⋅→s)→p
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B
→q+μ→p for all μ
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C
→q−(→q⋅→s→p⋅→s)→p
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D
→p⋅→s
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Solution
The correct option is C→q−(→q⋅→s→p⋅→s)→p relation, →r×→p=→q×→p ⇒→r×→p−→q×→p=0 ⇒(→r−→q)×→p=0 ⇒(→r−→q) and →p are parallel ∴→r−→q=λ→p ⇒→r=λ→p+→q…(1)
Now, ⇒→r⋅→s=0 ⇒(λ→p+→q)⋅→s=0 ⇒λ=−→q⋅→s→p⋅→s…(2)
Putting λ from (2) into (1), we get →r=−→q⋅→s→p⋅→s→p+→q ∴→r=→q−(→q⋅→s→p⋅→s)→p