𝜋 0 0 𝜋 2 s i n c o s d d .
find the volume under the surface 𝑧 = 4 𝑥 𝑦 over the rectangle 𝑅 = [ 0 , 1 ] × [ 0 , 1 ] .
find the volume under the surface 𝑧 = 𝑥 + 𝑦   over the rectangle 𝑅 = [ 0 , 1 ] × [ 0 , 1 ] .
find the volume under the surface 𝑧 = 𝑥 + 𝑥 𝑦 + 𝑦 4 3 of the rectangular prism with base 𝑅 = [ 1 , 2 ] × [ 0 , 2 ] .
find the volume under the surface 