Let $f:\mathbb{R}\to\mathbb{R}$ be a differentiable function that satisfies the relation $f(x+y)=f(x)+f(y)-1,\forall x,y\in\mathbb{R}$. If $f'(0)=2$, then $|f(-2)|$ is equal to ___________.
Answer (integer)
3
Solution
$f(x+y)=f(x)+f(y)-1$
<br/><br/>
$$
\begin{aligned}
& f^{\prime}(x)=\lim _{h \rightarrow 0} \frac{f(x+h)-f(x)}{h} \\\\
& f^{\prime}(x)=\lim _{h \rightarrow 0} \frac{f(h)-f(0)}{h}=f^{\prime}(0)=2 \\\\
& f^{\prime}(x)=2 \Rightarrow d y=2 d x \\\\
& y=2 x+C \\\\
& \mathrm{x}=0, \mathrm{y}=1, \mathrm{c}=1 \\\\
& \mathrm{y}=2 \mathrm{x}+1 \\\\
& |f(-2)|=|-4+1|=|-3|=3
\end{aligned}
$$
About this question
Subject: Mathematics · Chapter: Differentiation · Topic: Derivatives of Standard Functions
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