20.06.2013 Views

pdf (it, 2.898,97 KB, 25/01/13)

pdf (it, 2.898,97 KB, 25/01/13)

pdf (it, 2.898,97 KB, 25/01/13)

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

a <br />

(−∞, 0] a <br />

[0, +∞)<br />

˙x = 0 <br />

R := {(t, x(t)) : ˙x(t) > 0} = {(t, x) : t < x 2 },<br />

<br />

˙t = 1<br />

˙x = t − x 2<br />

R (˙t, ˙x) (t,x)∈R = (1, 0) R<br />

<br />

˙x <br />

x → +∞<br />

x ′′ = 1 − 2xx ′ = 1 − 2x(t − x 2 ) <br />

γ := {(t, x) : x ′′ = 0} = {(t, x) : 1 − 2xt + 2x 3 } = {(t, x) : t = 1/(2x) + x 2 }.<br />

γ t = t(x) = 1/(2x) + x 2 t = x 2 x → +∞ x → 0 ± <br />

±∞ x > 0 R x <br />

− 3 1/2 x x < 0 R 2 \ γ <br />

<br />

<br />

<br />

Q0 := {(t, x) : x ′′ < 0, x > 0, t > 0} = {(t, x) : 1 − 2xt + 2x 3 < 0 x > 0, t > 0}<br />

Q1 := {(t, x) : x ′′ > 0} = {(t, x) : 1 − 2xt + 2x 3 > 0}<br />

Q2 := {(t, x) : x ′′ < 0, x < 0} = {(t, x) : 1 − 2xt + 2x 3 < 0, x < 0}.<br />

<br />

<br />

γ <br />

F (t, x) = 0 F (t, x) = 1 − 2xt + 2x 3 (t, x) ∈ γ <br />

ˆn(t, x) = ±∇F (t, x) = ∓(2x, 2t − 6x 2 ) <br />

Q0 Q1 Q2<br />

Q0 Q0 <br />

∂Q0 x > 0 Q0 ˆn0(t, x) =<br />

(2x, 2t − 6x 2 )<br />

Q2 Q2 <br />

∂Q2 x < 0 Q2 ˆn2(t, x) =<br />

(2x, 2t − 6x 2 ) = ˆn0(t, x)<br />

Q1 ˆn1(t, x) = −n0(t, x) = −(2x, 2t − 6x 2 )<br />

ˆni · (1, ˙x) ∂Qi<br />

ˆn0 · (1, ˙x) t=1/(2x)+x 2 = [2x + (t − x 2 )(2t − 6x 2 )] t=1/(2x)+x 2 = 2x + 1<br />

2x<br />

= 2x + 1 1 3<br />

+ −<br />

2x2 x x<br />

1<br />

= > 0.<br />

2x2 ˆn2 · (1, ˙x) t=1/(2x)+x2 = ˆn0 · (1, ˙x) t=1/(2x)+x2 = 1<br />

> 0.<br />

2x2 ˆn1 · (1, ˙x) t=1/(2x)+x2 = −ˆn0 · (1, ˙x) t=1/(2x)+x2 = − 1<br />

< 0.<br />

2x2 <br />

1<br />

x + 2x2 − 6x 2

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!