Question
If θ=tan−1d1+a1a2+tan−1d1+a2a3+⋯+tan−1d1+an−1an, where a1,a2,a3,⋯an are in A.P. with common difference d, then tanθ=
Answer: Option A
:
A
θ=tan−1a2−a11+a1a2+tan−1a3−a21+a2a3+⋯+tan−1an−an−11+an−1an
=(tan−1a2−tan−1a1)+(tan−1a3−tan−1a2)+⋯+tan−1an−an−11+an−1an+⋯+(tan−1an−tan−1an−1)
=tan−1an−tan−1a1
=tan−1an−a11+a1an=tan−1(n−1)d1+a1an
∴tanθ=(n−1)d1+a1an
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:
A
θ=tan−1a2−a11+a1a2+tan−1a3−a21+a2a3+⋯+tan−1an−an−11+an−1an
=(tan−1a2−tan−1a1)+(tan−1a3−tan−1a2)+⋯+tan−1an−an−11+an−1an+⋯+(tan−1an−tan−1an−1)
=tan−1an−tan−1a1
=tan−1an−a11+a1an=tan−1(n−1)d1+a1an
∴tanθ=(n−1)d1+a1an
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