A non-zero vector →a is parallel to the line of intersection of the plane determined by the vectors ^i,^i+^j and the plane determined by the vectors ^i−^j,^j+^k. The angle between →a and the vector ^i−2^j+2^k is
A
π4
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B
π3
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C
π6
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D
π2
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Solution
The correct option is Bπ4 P1 is plane by ^i,^i+^i →r1=^i+λ(^j) P2 in plane by ^i−^j,^j+^k →r2=^i−^j+μ(−^i+2^j+^k) →r1=→r2 ^i+λ^i=(1−μ)^i+(2μ−1)^i+μ^k μ=0 λ=−1 So →a=k(^i−^j) →a−(^1−2^j+2^k)=|→a|∣∣^i−2^j+2^k∣∣cosθ k(1+2)3=k√2cosθ cosθ=1√2 θ=π4