# Math Help - limits and continuity

1. ## limits and continuity

1a)Do these functions have limits.If the limit exists, find it with justification, if not explain why not

i) f(x,y) =x²-y²/x²+y²
ii) f(x,y) =x³-y³/x²+y²
iii) f(x,y) =xy/|x|+|y|
iv) f(x,y) =1-√(1-x²)/x²+ xy+y²
v) f(x,y) =y³x/y^6+x²

im having problems finding the limits especially iii) and iv). i know that you can prove a limit doesn't exist by demonstration but how do you justify it if it does exist

b) Let f be a real valued function of two real variables defined by:

f(x,y) ={2x sin y/ x²+y² if y >x
sin(x+y) if y≤x
Determine the points at which f is continuous.

2. Let's look at (iii). I claim the limit is zero: that is, for all epsilon > 0 there exists delta > 0 such that if 0 < sqrt(x^2+y^2) < epsilon then | xy(|x|+|y|) | < delta.
I claim we can take delta = epsilon. If 0 < sqrt(x^2+y^2)<epsilon, then |x| and |y| are less than epsilon and one of them, say x, is non-zero. Then |x|.|y|/(|x|+|y| < epsilon. |x|/(|x| + epsilon) < epsilon as claimed.