The lengths of the diagonals of a parallelogram constructed on the vectors →p=2→a+→b & →q=→a−2→b, where →a & →b are unit vectors forming an angle of 60∘ are
A
3 & 4
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B
√7 & √13
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C
√5 & √11
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D
None
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Solution
The correct option is C√7 & √13 In the above parallelogram, the diagonals are given by →p+→q and →p−→q.
Thus, the diagonals are 3→a−→b and →a+3→b
Modulus of these vectors are respectively given by √9a2−6→a.→b+b2 & √a2+6→a.→b+9b2
Since →a & →b are unit vectors, the modulii become √9−6×cos60o+1 & √1+6×cos60o+9