You will show that lim(x,y)→(0,0)f(x,y)does not exist when f(x,y)=5x^2-2y^2/x^2+4y^2 by finding two lines of approach to (0,0)for which f(x,y) has different limits.
Select two lines y=M1x and y=M2x.
Let L1=lim(x,y)→(0,0) f(x,y) along the line y=M1x.
Let L2=lim(x,y)→(0,0) f(x,y)along the line y=M2x.
Pick M1 and M2 so that L1≠L2.Enter the four numbers as a quartet (M1,L1,M2,L2).