(1) Along the x-axis, we have y = 0, so that
[tex]\displaystyle\lim_{(x,y)\to(0,0)} \frac{3x^2}{4x^2+4y^2} = \lim_{x\to0} \frac{3x^2}{4x^2} =\lim_{x\to0}\frac34= \frac34[/tex]
(2) Along the y-axis, we take x = 0, then
[tex]\displaystyle\lim_{(x,y)\to(0,0)} \frac{3x^2}{4x^2+4y^2} = \lim_{y\to0} \frac0{4y^2} = 0[/tex]
(3) Along the line y = mx, we have
[tex]\displaystyle\lim_{(x,y)\to(0,0)} \frac{3x^2}{4x^2+4y^2} = \lim_{x\to0} \frac{3x^2}{4x^2+4(mx)^2} = \lim_{x\to0}\frac{3x^2}{4x^2+4m^2x^2} = \frac3{4+4m^2}[/tex]
which means the limit is dependent on the slope of the line m.
(4) nonexistent
