The formula of the area of the trapezoid:
[tex]A=\dfrac{b_1+b_2}{2}\cdot h[/tex]
We have:
[tex]b_1=5\sqrt2;\ b_2=3\sqrt2;\ h=4\sqrt2[/tex]
Substitute:
[tex]A=\dfrac{5\sqrt2+3\sqrt2}{2}\cdot4\sqrt2=\dfrac{5\sqrt2}{2}\cdot4\sqrt2=\dfrac{5\cdot4\cdot\sqrt2\cdot\sqrt2}{2}\\\\=\dfrac{20\cdot2}{2}=20[/tex]
Used: [tex]\sqrt{a}\cdot\sqrt{a}=a[/tex]
