一、(50%) CALCULUS 1. (10%) Let $f(x)$ be a differentiable function as shown in Figure 1. It needs to compute the integral $\int_{a}^{b} f(x)dx$. For some reason, the integration is not possible. We decide to linearize $f(x)$ at $x = a$ and use the trapezoidal area $A$ to approximate the integral, i.e. $\int_{a}^{b} f(x)dx \approx A$. Please find the area $A$.