Question

Answer 1

AB//CD

=>\(\frac{OA}{OC}=\frac{OB}{OD}=\frac{AB}{CD}=\frac{10}{20}=\frac12\)

\(\frac{OA}{OC}=\frac12\)

=>\(\frac{S_{OAB}}{S_{OBC}}=\frac12\)

=>\(S_{OAB}=\frac{100}{2}=50\left(\operatorname{cm}^2\right)\)

\(\frac{OB}{OD}=\frac12\)

=>\(\frac{S_{OAB}}{S_{OAD}}=\frac12\)

=>\(S_{OAD}=50\times2=100\left(\operatorname{cm}^2\right)\)

Vì \(\frac{OA}{OC}=\frac12\)

nên \(\frac{S_{OAD}}{S_{ODC}}=\frac12\)

=>\(S_{ODC}=100\times2=200\left(\operatorname{cm}^2\right)\)

\(S_{ABCD}=S_{OAB}+S_{OBC}+S_{OAD}+S_{OCD}\)

\(=50+100+100+200=450\left(\operatorname{cm}^2\right)\)