## Calculus: Early Transcendentals 8th Edition

Given: $\lim\limits_{(x,y,z) \to (0,0,0)}\frac{xy+yz^{2}+xz^{2}}{ {x^{2}+y^{2}+z^{4}}}$ We can approach the points (0, 0, 0) in space through the co-ordinate axes, through a co-ordinate plane, or through symmetrical or unsymmetrical lines. Now, approach the point (0, 0, 0) along the x-axis. To evaluate limit along x-axis; put $y=0,z=0$ $=\lim\limits_{(x,y,z) \to (0,0,0)}\frac{0+0+0}{ {x^{2}+0^{2}+0^{4}}}=\frac{0}{x^{2}}=0$ Approach the point (0, 0, 0) along the curve where $x=y$ and $x=z^{2}$ $\lim\limits_{(x,y,z) \to (0,0,0)}\frac{x^{2}+x^{2}+x^{2}}{ {x^{2}+x^{2}+x^{2}}}$ $=\lim\limits_{(x,y,z) \to (0,0,0)}\frac{3x^{2}}{3x^{2}}$ $=1$ For a limit to exist, all the paths must converge to the same point. Hence, the limit does not exist.