9000106305

Find the area of the triangle $ABS$. Only first two coordinates of the point $B=[2;0;?]$ are given and $B$ lies in the plane $\alpha$ defined by the equation $$\alpha :2x+y-z-5=0.$$ The point $S$ is the intersection point of the plane $\alpha$ and the line $k$ which is perpendicular to $\alpha$ and passes through the point $A=[0;0;1]$.