For the first function:
$f(x, y) = \int_{x}^{y} \sin \left(\frac{1}{t}\right) dt$
We need to compute $f_x$ and $f_{xx}$.
Recall the Fundamental Theorem of Calculus, Part 1: If $F(x) = \int_{a}^{x} g(t) dt$, then $F'(x) = g(x)$.
Also, if $F(x) = \int_{x}^{a}
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