If x=a1/2+a−1/2,y=a1/2−a−1/2, then value of (x4−x2y2−1)+(y4−x2y2+1).
A
9
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B
25
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C
14
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D
16
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E
None of these
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Solution
The correct option is D16 x=a1/2+a−1/2.....(1)y=a1/2−a−1/2.....(2)then(x4−x2y2−1)+(y4−x2y2+1)x4−x2y2+1+y4−x2y2+1x4+y4−2x2y2(x2)2+(y2)2−2x2y2(x2−y2)2[∵x2−y2=(x−y)(x+y)x2−2xy+y2=(x−y)2][(x−y)(x+y)]2=?........(3)AddingandsubstractingbothequationrespectivelyAddingx=a12+a−12y=a12−a−12x+y=2a12Substractingx=a12+a−12y=a12−a−12x−y=2a−12puttingthevalueof(x+y)and(x−y)ineq(3)[(2a−12)(2a12)]2[4a0]2=16[∵a0=1]