Double Integral
Functions of two variables: f(x, y), f(u,
v), …
Small changes: Δxi,
Δyi
Regions of integration: R, S
Polar coordinates: r, θ
Area: A
Surface area: S
Volume of a solid: V
Mass of a lamina: m
Density: ρ(x, y)
First moments of inertia: Ix,
Iy, I0
Charge of a plate: Q
Charge density: σ(x, y)
Coordinates of center of mass:
Average of a function: μ
- Definition of Double Integral
The double integral over a rectangle [a, b] × [c, d]
is
defined to be
Where (xi - 1, xi) × (yj- 1, yj), and Δxi = xi – xi – 1,
Δyj
= yj – yj – 1.
Figure
The double integral over a gereral region R is
Where rectangle [a, b] × [c, d] contains R,
g(x, y) = f(x, y) if f(x, y) is in R and g(x, y) = 0
otherwise.
Figure
Figure
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