f(x)=x1loge(1+x),x=0
f′(x)=x21+xx−ln(1+x)=x2(1+x)x−(1+x)ln(1+x)
Let g(x)=x−(1+x)ln(1+x)
g′(x)=−ln(1+x)
\Rightarrow {g}^{'}(x){\begin{matrix}>0 & \forall x\in (-1,0) \\ <0 & \forall x\in (0,\infty )\end{matrix}
gmax at x=0⇒g(0)=0 is the maximum value
So, g(x)<0∀x∈(−1,∞)⇒f′(x)<0∀x∈(−1,∞)
Hence, f(x) is decreasing ∀x∈(−1,∞)