$r$ more variables. For

$3-$space $is$

$7-8$ Show that the $limit$ does not exist $by$ considering the $limits$

$as(x,y)(0,0)$ along the coordinate axes.

$(a)\underset{(x,y)(0,0)}{lim}\frac{3}{x^2+2y^2}$

$(b)\underset{(x,y)(0,0)}{lim}\frac{x+y}{2x^2+y^2}$

$(a)\underset{(x,y)(0,0)}{lim}\frac{x-y}{x^2+y^2}$

$(b)\underset{(x,y)(0,0)}{lim}\frac{cosxy}{x^2+y^2}$