If a>0 and P(−a,0),Q(a,0) and R(1,1) are three points such that ∣∣(PR)2−(QR)2∣∣=12, then
A
(PR)2=17
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B
(QR)2=5
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C
(PR)2=5
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D
(QR)2=17
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Solution
The correct options are A(PR)2=17 B(QR)2=5 |(1+a)2+1−[(1−a)2+1]|=12 |4a|=12 4a=12 or 4a=−12 ∴a=3,−3 Since a>0 ∴a=3 Now (PR)2=(1+3)2+1 (PR)2=17 (QR)2=(1−3)2+1 (QR)2=5