find the limits by referring details when you solve them when (x,y)goes to (0,0) :

1_ lim (x^2 + y^2 ) sin ( 1\(x ^2 + y^2))(i'm trying but i don't know )

2- lim e ^ -1 over (sqr root for x^2 + y^2)

3- lim { e ^ -1 over (sqr root for x^2 + y^2) } over (sqr root for x^2 + y^2)

4- lim 1- ( x^2 + y^2)\( x^2 + y^2)

5- lim y ln ( x^2 + y^2)

when i solve the limit #4 first i substitute (0,0) the answer 1\0 i know that the limit doesn't exist but i don't know how i can show that ???

in #5 when i translate xy-coordinate to r,theta i can't complete