%TiKZ radians confuses \tkzMarkAngle and friends
\begin{tikzpicture}
  \tikzmath{\Size=5;};

  %Must be first...
  \filldraw[white](\Size,\Size) -- (-\Size,\Size) -- (-\Size,-\Size) -- (\Size,-\Size) -- cycle;

  \draw[-Latex] (-\Size,0) -- (\Size,0) node [right] {$x$};
  \draw[-Latex] (0,-\Size) -- (0,\Size,0) node [above] {$y$};
  
  \tikzmath{\a=2;};
  \tikzmath{\aa=-2;};
  \tikzmath{\b=0.5;};
  \tikzmath{\bb=0.5;};

  \tikzmath{\x=-4;};
  \tikzmath{\xx=4;};

  \filldraw [name path=l1]
  ($(\x,\a*\x+\b)$)
  circle(2pt)
  node [below] {$y=\a\cdot x+\b$}
  --
  ($(\xx,\a*\xx+\b)$)
  circle(1pt);
  
  \filldraw [name path=l2]
   ($(\x,\aa*\x+\bb)$) 
  circle(3pt)
  node [above] {$y=\aa\cdot x+\bb$}
  --
  ($(\xx,\aa*\xx+\bb)$)
  circle(1pt);

  \path [name intersections={of=l1 and l2,by=X}];
  \filldraw (X) circle(1pt) node [right] {$X$};

  \draw [name path=c1] (0,0) circle(4);
  \draw [name path=c2] (0,0) circle(2);

  
  \path [name intersections={of=l1 and c1,by=X1}];
  \filldraw (X1) circle(1pt) node [above] {$X$};

  %Several intersection points
  \draw [name intersections={of=l1 and c2, total=\n}]  
     \foreach \i in {1,...,\n}{
        (intersection-\i)
       circle(2pt)
       node [anchor=south west]   {$~X_\i$}
     };
        
\end{tikzpicture}