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Find all $m$ and $b \in \mathbb{R}$ st $f(x)$ is differentiable at $x = 1$

$f(x) = \begin{cases} mx + b & \text{for $x \le 1$} \\[6pt] \tan\left(\frac{x\pi}{4}\right) & \text{for $1

A couple of things caught me off guard with this. First, I am used to seeing one of the variable disappear when I set $x$ equal to the point where the two parts of the function meet; however, here we get:

$m + b = \tan(\frac{\pi}{4}) = 1$ in order for the function to be continuous at $x = 1$.

For it to be differentiable at $x = 1$

$m = \frac{\pi}{4\cos^2(\frac{\pi}{4})} = \frac{\pi}{2}$

$\therefore m = \frac{\pi}{2},\quad b = \frac{2 - \pi}{2}\ ?$

I wasn't sure if this was right or if I got all the answers.

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    There is only one solution because there is only one line that "continues" a function from (0,1) to R: the function's tangent in 1.2012-04-30

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