222. Calculate the area of the curvilinear trapezoid bounded by the lines $f(x)=1 / x, x=1, x=2, y=0$.
Solution. Let's construct a trapezoid (Fig. 142). Determine the antiderivative of the function \( f(x) = 1 / x \):

$$
\int \frac{1}{x} d x = \ln x + C
$$

One of the antiderivatives when \( C = 0 \) is \( F(x) = \ln x \). Then the desired area can be found using formula (1):

$$
S = F(2) - F(1) = \ln 2 - \ln 1 = \ln 2 \approx 0.7 \text{ (sq. units). }
$$