The cross-section of a road partly in banking and partly in cutting is shown in the following figure, the area of the shaded portion is:
1
\(\frac{1}{2} \times \frac{{{{\left( {b - rd} \right)}^2}}}{{r - s}}\)
2
\(\frac{1}{3} \times \frac{{{{\left( {b - rd} \right)}^2}}}{{r - s}}\)
3
\(\frac{1}{2} \times \frac{{{{\left( {b + rd} \right)}^2}}}{{r - s}}\)
4
\(\frac{1}{3} \times \frac{{{{\left( {b + rd} \right)}^2}}}{{r - s}}\)