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Câu hỏi: Diện tích hình phẳng gạch chéo trong hình vẽ được tính theo công thức nào?
A. $\int\limits_{a}^{c}{\left[ \left| g\left( x \right) \right|-\left| f\left( x \right) \right| \right]dx}$.
B. $\int\limits_{a}^{b}{\left[ f\left( x \right)-g\left( x \right) \right]dx}+\int\limits_{b}^{c}{\left[ g\left( x \right)-f\left( x \right) \right]dx}$.
C. $\int\limits_{a}^{b}{\left[ g\left( x \right)-f\left( x \right) \right]dx}+\int\limits_{b}^{c}{\left[ f\left( x \right)-g\left( x \right) \right]dx}$.
D. $\left| \int\limits_{a}^{c}{\left[ g\left( x \right)-f\left( x \right) \right]dx} \right|$.
B. $\int\limits_{a}^{b}{\left[ f\left( x \right)-g\left( x \right) \right]dx}+\int\limits_{b}^{c}{\left[ g\left( x \right)-f\left( x \right) \right]dx}$.
C. $\int\limits_{a}^{b}{\left[ g\left( x \right)-f\left( x \right) \right]dx}+\int\limits_{b}^{c}{\left[ f\left( x \right)-g\left( x \right) \right]dx}$.
D. $\left| \int\limits_{a}^{c}{\left[ g\left( x \right)-f\left( x \right) \right]dx} \right|$.
Ta có: $S=\int\limits_{a}^{b}{\left[ g\left( x \right)-f\left( x \right) \right]dx}+\int\limits_{b}^{c}{\left[ f\left( x \right)-g\left( x \right) \right]dx}$.
Đáp án C.