How can I prove that $$\displaystyle x-\frac {x^2} 2 < \ln(1+x)$$ for any $x>0$
I think it's somehow related to Taylor expansion of natural logarithm, when:
$$\displaystyle \ln(1+x)=\color{red}{x-\frac {x^2}2}+\frac {x^3}3 -\cdots$$
Can you please show me how? Thanks.
Answer
Hint:
Prove that $\ln(1 + x) - x + \dfrac{x^2}2$ is strictly increasing for $x > 0$.
edit: to see why this isn't a complete proof, consider $x^2 - 1$ for $x > 0$. It's strictly increasing; does that show that $x^2 > 1$? I hope not, because it's not true!
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