11.a = ∫ (2x-x2) dx (0 to 2)-∫ (x-x 2) dx (0 to1) = 7/6;

V = ∫ π [(2x) 2-(x 2) 2) dx (0 to 2)-∫π [x 2-(x 2) 2) dx (0 to 1)=62π/ 15.

12.du =(ζu/ζx)dx+(ζu/ζy)dy =(f 1 ' * 2x+F2 ' * y)dx+(f 1 ' * 4y+F2 ' * x)dy

13.ζz/ζx=[y/(2√x)]/√[ 1-(y√x)^2]=y/(2√[x-x^2y^2)]，

ζz/ζy=√x/√[ 1-(y√x)^2]=√x/√( 1-xy^2)

14. ∫ x/y2ddxdy = ∫ (1to 2)dx∫( 1/x to x) x/y 2dy = ∫ (1 to 2).