Question

Answer 1

Bài 11:

a: Diện tích hình thang ABCD là:

\(S_{ABCD}=\dfrac{1}{2}\cdot\left(AB+CD\right)\cdot AD\)

\(=\dfrac{1}{2}\cdot25\cdot\left(50+30\right)\)

\(=\dfrac{25}{2}\cdot80=25\cdot40=1000\left(cm^2\right)\)

b: Diện tích tam giác ADC là:

\(S_{ADC}=\dfrac{1}{2}\cdot AD\cdot DC=\dfrac{1}{2}\cdot25\cdot50=625\left(cm^2\right)\)

Ta có: \(S_{ADC}+S_{ABC}=S_{ABCD}\)

=>\(S_{ABC}+625=1000\)

=>\(S_{ABC}=375\left(cm^2\right)\)