Is there any way to solve the inequation: ${e^{2x - 1}} \ge 2x$ without plotting the graph?
How to solve this inequation without plotting the graph?
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inequality
1 Answers
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All you need to know is $e^x \geq 1 + x$, $\forall x \in \mathbb{R}$
Equality holds when $x=0$
To prove $e^x \geq 1 + x$, $\forall x \in \mathbb{R}$, consider $f(x) = e^x - 1 -x$
f'(x) = e^x - 1 = 0 \Rightarrow, $x=0$ is an extremum.
Further f''(x) = e^x > 0, $\forall x \in \mathbb{R}$
Hence, $x=0$ is a minimum
Hence, we get $f(x) \geq f(0)$, $\forall x \in \mathbb{R}$
Hence, $e^x - 1 - x \geq 0$, $\forall x \in \mathbb{R}$
Hence, $e^x \geq 1 + x$, $\forall x \in \mathbb{R}$
Replacing $x$ by $2x-1$, we get $e^{2x-1} \geq 1 + (2x-1) = 2x$, $\forall x \in \mathbb{R}$
Equality holds when $2x-1=0$ i.e. when $x = \frac{1}{2}$