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Differential Geometry section 1
Curves and Surfaces
25
Mathematics
Undergraduate 4
03/02/2010

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Term
Regular Surface
Definition
a subset S in R3, for each p in S, there exists a Neighborhood V in R3 s.t.
1. X is differentiable
2. x is a homeomorphism
3. for all q in U, the differential dx_q: R2 -> R2 is 1-1
Term
Homeomorphism
Definition
there exists x^-1: V int S -> U which is continuous
Term
if f is differentiable, (x,y,f(x,y)) is what?
Definition
a regular surface
Term
Critical Point + Value
Definition
dF_p:Rn->Rm is not a surjective (onto) mapping.

f'(x_0) = 0

the image F(p) in Rm of a crit point
Term
Regular Value
Definition
Not a crit Value
Term
If f is D'able, and a in f(U) is a regular surface, then...
Definition
f^-1(a) is a regular surface
Term
If x is 1-1, p in a regular surface, and holds conditions 1 + 3, then..
Definition
x^-1 is continuous
Term
Change of parameters is a...
Definition
diffeomorphism
Term
diffeomorphic
Definition
there exists a differentiable map Q:S1->S2 with a differentiable inverse Q^-1: S2->S1
Term
regular curve
Definition
subset of C in R3 s.t. for all p in C, there exists a Neighborhood V of p in R3 and a d able homeomorphism alpha:I in R -> V int C s.t. d'alpha is 1-1 for all t in I.
Term
X(u)is regular if
Definition
dx_q R2->R3 is 1-1 for all q in U
Term
if x is a regular parametrized surface, and q in U, then...
Definition
there exists a Neighborhood V of q in R2 s.t. x(V) in R3 is a regular surface
Term
I_p on T_p(s) is called the 1st fundamental form of the regular surface s in R3 at p in S s.t. ...
Definition
"I_p (w) = _p = |w|^2 >= 0"
Term
I_p(a'(0)) =
Definition
E*(u')^2 + 2 F*u'v' + G(v')^2
Term
Arc length of a parametrized a:I->S =
Definition
s(t) = int(|a'(t)|dt, 0,t)
= int((I(a'(t))^(1/2))dt, 0,t)

if u, v apply...
= Int((E(u')^2 + 2*F*u'*v' + G(v')^2)^(1/2)dt,0,t)
Term
Orthogonal curves iff
Definition
F(u,v) = 0 for all u,v
Term
area of parallelogram:
Definition
|x_u V x_v|
Term
area of regular surface
Definition
=Int(Int( |x_u V x_v| du,dv))_Q

,Q = x^-1(R)
Term
|x_u V x_v|
Definition
(EG - F^2)^(1/2)
Term
Gauss map N(q) =
Definition
(x_u V x_v) / |x_u V x_v| (q), q in x(u)
Term
II_p in T_p(s) =

(Second Fundamental Form of S at p)
Definition
"-"
Term
normal curvature of C in S at p,

K_n=
Definition
=K * cos (theta),

for cos(theta) = ,
n = normal vector to C
N = normal vector to S
Term
for all alpha(s) in S, @ p, having the same tangent line...
Definition
have the same normal curvatures at this point
Term
K_1 is ...
K_2 is ...
Definition
1 - maximum normal curvature
2 - minimum are principal curvatures

e_1, e_2 are their directions called principal directions @ p
Term
E(u,v)=
F(u,v)=
G(u,v)=
Definition
"E = < x_u, x_u >
F = < x_u, x_v >
G = < X_v, X_v >"
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