Consider 9 circles each arranged at the center of cells of a 2-D matrix of shape 3*3. Draw 3 straight lines without removing pen from paper such that each of the 9 circles is in contact with at least one line.
Solution:
A similar problem is present here Connect 9 dots using 4 lines.
The difference from above problem is that here there are 9 circles not 9 points. Also we can only draw 3 lines.
One such way of doing what is asked is:
The thing to notice is that since these are circles, not points, we can draw a line that is tangent to the circle. There is no need to pass the line through the center as the only contact with the circle is required.