設(shè)D是由不等式|x|+|y|≤1所確定的有界區(qū)域,則二重積分|x|dxdy的值是:()
A.0
B.1
C.2/3
D.1/3
設(shè)D是矩形區(qū)域:0≤x≤π/4,-1≤y≤1,則xcos2xydxdy等于:()
A.0
B.-1/2
C.1/2
D.1/4
設(shè)D是兩個(gè)坐標(biāo)軸和直線x+y=1所圍成的三角形區(qū)域,則xydσ的值為:()
A.1/2
B.1/6
C.1/24
D.1/12