Answer
$\dfrac{3}{2} \ sq. unit$
Work Step by Step
We are given that $f(x)=\int_1^2 x \ dx$
Here. the area of a trapezoid is equal to $A= \int_1^2 (x) \ dx$
$=\dfrac{1}{2} \times (a+b) \times Height$
$=\dfrac{1}{2} (1+2)(2-1)$
Thus, $\int_1^2 (x) \ dx=\dfrac{3}{2} \ sq. unit$
