What is the maximum number of parts a circle can be divided into by three straight lines?

If you think about this problem well, you will notice that the circle has absolutely nothing to do with it! We simply divide into parts a piece of the plane located inside the circle. Having understood this, we can do without even visual pictures in further reasoning! So, we draw the first straight. The second line must intersect with the first. Lines intersect only at one point, which means they will divide the plane into four parts. Now if we draw the third straight line intersecting the first two NOT through the point of their intersection, we get a plane divided into 7 parts! Otherwise there will be only 6!

Answer: into 7 parts.