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MULTIPLE INTEGRALS
CHANGEofVARIABLES
Change of Variables for Double Integrals
• assume C1 transformations for (u,v) → (x,y)
x = g(u,v), y = h(u,v)
for (u,v) ∈ S and (x,y) ∈ R;
• define Jacobian for transformation, by determinant
∂x ∂x
∂(x,y) ∂u ∂v ∂x∂y ∂x∂y
=∂y ∂y = − ;
∂(u,v) ∂u ∂v ∂u∂v ∂v∂u
• transformed double integral formula is
ZZ ZZ ∂(x,y)
f(x,y)dA = f(g(u,v),h(u,v)) dudv.
R S ∂(u,v)
TRIPLE INTEGRALS
CHANGEofVARIABLES
Change of Variables for Triple Integrals
• assumeC1 transformationsfor(u,v,w) → (x,y,z)
x = g(u,v,w), y = h(u,v,w), z = k(u,v,w)
for (u,v,w) ∈ S and (x,y,z) ∈ R;
• define Jacobian for transfomation, by determinant
∂x ∂x ∂x
∂u ∂v ∂w
∂(x,y,z) ∂y ∂y ∂y
=
∂(u,v,w) ∂u ∂v ∂w
∂z ∂z ∂z
∂u ∂v ∂w
= ∂x∂y∂z + ∂z∂x∂y + ∂y∂z∂x
∂u∂v∂w ∂u∂v∂w ∂u∂v∂w
−∂z∂y∂x −∂y∂x∂z −∂x∂z∂y;
∂u∂v∂w ∂u∂v∂w ∂u∂v∂w
• transformed triple integral formula is
ZZZ f(x,y,z)dV
R
ZZZ ∂(x,y,z)
= f(g(u,v,w),h(u,v,w),k(u,v,w) dudvdw.
S ∂(u,v,w)
2
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