Đổi: \(\dfrac{2}{5}m=4dm\)
Diện tích hình tam giác là:
\(\dfrac{\dfrac{1}{3}.4}{2}=\dfrac{2}{3}=0,67dm^2\)
Đ/s
\(S=\dfrac{\dfrac{1}{3}\cdot4}{2}=\dfrac{1}{3}\cdot2=\dfrac{2}{3}\left(dm^2\right)\)
\(\dfrac{2}{5}m=4dm\\ S=\dfrac{1}{3}\times4:2=\dfrac{2}{3}dm^2\)
\(S=\dfrac{\dfrac{1}{3}\times4}{2}=\dfrac{1}{3}\times2=\dfrac{2}{3}\left(dm^2\right)\)