Arc length of parabola between two points Well lets take a parabola of the equation $y = f(x)$  where $f(x)$ is obviously a $2^{nd}$ degree function.

Now lets take two points at $x=a$ and $x=b$ .
So can anyone please help me to find that curved arc length between the points $a$ and $b$?
Can we also extend this to any other equation other than a parabola??
Thanks!
 A: Let's write the parab as $y = ax^2 + bx + c$, and use $A$ and $B$ as the limit points instead of your $a$ and $b$. 
Arlength is then
$$
s = \int_A^B \sqrt{1 + (2ax + b)^2} dx,
$$
which is probably amenable to a substitution like 
$$
\tan t = 2ax + b\\
\sec^2 t dt = 2a dx 
$$
yeielding
$$
\int_{x=A }^B \sec^3(t) dt = \frac{1}{2} \left( \sec t \tan t + \ln |\sec t + \tan t| \right) |_{x = A}^{x = B}.
$$
Note that in the substitution, we can also write
$$
t = \arctan(2ax + b)
$$
so that the range $x = A$ to $x = B$ becomes 
$$
t = \arctan(2aA + b) \text{ to}\\
t = \arctan(2aB + b).
$$
You'll have to do the substitution and algebra in that final step for yourself. Hint: 
$$
\sec(\arctan(x)) = \sqrt{1+x^2}.
$$
To answer your second question, yes, you can compute arclength for other graphs...but not many. Surprisingly often the integral
$$
\int \sqrt{1 + f'(x)^2} dx
$$
turns out to not be easy to integrate in elementary terms (which is, I assume, what you're looking for; if not, then the integral itself is a general answer). The fact that it's so hard to make it work out nicely is a constant annoyance to calculus teachers. 
