If tan−1(x+1)+tan−1(x−1)=tan−1(831), then x is equal to
A
1/2
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B
-1/2
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C
1/4
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D
1
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Solution
The correct option is C 1/4 We have, tan−1[x+1+x−11(x+1)(x−1)]=tan−1831 ⇒2x1−(x2−1)=831⇒62x=16−8x2 ⇒8x2+62x−16=0⇒4x2+31x−8=0 ⇒4x2+32x−x−8=0⇒4x(x−8)−1(x+8)=0 ⇒(x+8)(4x−1)=0⇒x=−8.14 ∴x=14.Neglectingx=−8.as.x2−1<1