Dear Robrt, your understanding of my problem is right. I need the points where f(x,y) = constant. But there are infinite answers for it andfinite number of poins are attainable numerically. For this the the x and y should be meshed, here to 98 points (with intervals of 0.01). The plot of this points can be drawn easily using the command:
contourplot(f(x,y), y = 1.01 .. 1.99, x = 0.1e-1 .. 0.99, contours = [10,20,30,40,50], grid = [200, 200]);
but I am interested to find the poins and insert in a matrix (or array). Thank you for your help. But my problem is a function of two variables. For your example, the function is a one-variable function, since y is function of x itself.