16.3 The Fundamental Theorem for Line Integrals
8. Since Fx = 2x cos xy−x2y sin xy and Fy = x cos xy−x2y sin xy+
x cos xy, therefore F is conservative.
Z
xy cos xy + sin xy dx = 1
y(xy sin xy) + c = x cos xy + c 14.
F = ( y2
1 + x2, 2y tan−1x) = ∇(y2tan−1x) Z
C
F · T = y2tan−1x |(1,2)(0,0)= 4 ∗ π 4 20.
∂x(4xy − 9x4y2) = ∂y(2y2− 12x3y3) Z (3,2)
(1,1)
2y2− 12x3y3dx + 4xy − 9x4y2dy = 2xy2− 3x4y3 |(3,2)(1,1)= −1919 23. H F · T > 0, F is non-conservative.
24. H F · T = 0, F is conservative.
33. Qx = x2+ y2− 2x2 and Py = −(x2+ y2) + 2y2 Z
x2+y2=1
F · T = Z
(− sin θ, cos θ) · (− sin θ, cos θ) dθ = 2π 34.
∇(− c
| x |) = cx
| x |3 Z
C
−F · T = − Z
d(− c
| x |) = c
| x | |dd2
1= c(1 d2 − 1
d2) Gravitational work = GMm|x| |perihelionaphelion , Electrical work = Qq|x| |
1 2∗10−12 10−12
1