MHB Why Can't the Integral from 1 to x of $\sqrt{1+{t}^{4}}$ be Replaced with x?

[karush]

got really hefty answers with the calculator but can t be replaced with x

$$F\left(x\right)=\int_{1}^{x}\sqrt{1+{t}^{4}} \,dt$$

I assume it is just the derivative

$\sqrt{1+{t}^{4}}$

 

[Opalg]

got really hefty answers with the calculator but can t be replaced with x

$$F\left(x\right)=\int_{1}^{x}\sqrt{1+{t}^{4}} \,dt$$

I assume it is just the derivative

$\sqrt{1+{t}^{4}}$

You haven't said what the problem is. If it is to find the derivative $F'(x)$ then the answer is $\sqrt{1+{x}^{4}}$ (with an $x$, not a $t$).