Answer
$y=\int_{1}^{x} \sqrt {1+t^2}dt -2$
Work Step by Step
Given: $\dfrac{dy}{dx}=\sqrt {1+t^2}$
$\implies \dfrac{d}{dx} [\int_{1}^{x} \sqrt {1+t^2} dt] -2=\sqrt {1+t^2}$
$\implies y(1)=\int_{1}^{1} \sqrt {1+t^2} dt $
$\implies y(1)=-2$
Hence, $y=\int_{1}^{x} \sqrt {1+t^2}dt -2$