If fn−1(x)=ln(fn(x))∀n∈N and f0(x)=x−1, then ddx(fn(x)) is
A
fn(x)⋅fn−1(x)
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B
fn(x)⋅fn−1(x)⋅fn−2(x)⋯f1(x)
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C
fn−1(x)⋅ddx(fn−1(x))
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D
fn(x)⋅ddx(fn−1(x))
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Solution
The correct options are Bfn(x)⋅fn−1(x)⋅fn−2(x)⋯f1(x) Dfn(x)⋅ddx(fn−1(x)) fn−1(x)=ln(fn(x)) Diffrentiating f′n−1(x)=1fn(x)×f′n(x) f′n(x)=fn(x).f′n−1(x) Replace n with n−1
f′n−1(x)=fn−1(x).f′n−2(x) f′n(x)=fn(x).fn−1(x).fn−2(x)......f1(x).f′0(x)....(i) f0(x)=x−1⇒f′0(x)=1 From (i) f′n(x)=fn(x).fn−1(x).fn−2(x).......f1(x)