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A =]0, +∞[×]0, +∞[ f : A → R<br />

<br />

f(x, y) = x2 − y 2 + 2xy<br />

y 2 + 3xy + x .<br />

lim<br />

(x,y)→(0,0)<br />

(x,y)∈A<br />

f(x, y).<br />

x = y <br />

2x<br />

f(x, x) =<br />

2<br />

x2 + 3x2 2x<br />

=<br />

+ x 4x + 1 .<br />

0 x → 0 0 y = mx <br />

x = my <br />

0<br />

y = mx x = my <br />

x = my 2 m > 0 <br />

f(my 2 , y) = m2 y 4 − y 2 + 2my 3<br />

y 2 + 3my 3 + my 2<br />

= m2y2 − 1 + 2my<br />

1 + 3my + m<br />

<br />

lim<br />

y→0 + f(my2 , y) = − 1<br />

1 + m<br />

m > 0 <br />

<br />

lim<br />

(x,y)→(0,0)<br />

x,y∈A<br />

f(x, y)

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