The intervals of monotonicity of the function $y=x^2-\log_e|x|.(x≠0)$ |
$(-∞,\frac{-1}{\sqrt{2}})∪(0,\frac{1}{\sqrt{2}})$ $(∞,\frac{1}{\sqrt{2}})∪(0,\frac{-1}{\sqrt{2}})$ $(∞,\frac{1}{\sqrt{2}})∪(0,\frac{1}{\sqrt{2}})$ $(-∞,-\frac{1}{\sqrt{2}})∪(0,\frac{-1}{\sqrt{2}})$ |
$(-∞,\frac{-1}{\sqrt{2}})∪(0,\frac{1}{\sqrt{2}})$ |
Let $y=x^2-\log_e|x|$ $f(x)=\left\{\begin{matrix}x^2-\log_e(-x),&x<0\\x^2-\log(x),&x>0\end{matrix}\right.$ $⇒f'(x)=\left\{\begin{matrix}2x-\frac{1}{(-x)}(-1),&x<0\\2x-\frac{1}{x},&x>0\end{matrix}\right.$ $∴f'(x)=2x-\frac{1}{x}$ for all $x(x≠0)$ $f'(x)=\frac{2x^2-1}{x}$ $f'(x)=\frac{(\sqrt{2}-1)(\sqrt{2}+1)}{x}$ Using number line rule, as shown in figure it gives $f'(x)>0$ when $x∈(-\frac{1}{\sqrt{2}},0)(\frac{1}{\sqrt{2}},∞)$ and $f'(x)<0$ when $x∈(-∞,-\frac{1}{\sqrt{2}})(0,\frac{1}{\sqrt{2}})$ ∴ f(x) is increasing when $x∈(-\frac{1}{\sqrt{2}},0)(\frac{1}{\sqrt{2}},∞)$ and decreasing when $x∈(-∞,-\frac{1}{\sqrt{2}})(0,\frac{1}{\sqrt{2}})$ |