Secant line and diameter of a circle A secant line incident to a circle at points $A$ and $C$ intersects the circle's diameter at point $B$ with a $45^\circ$ angle. If the length of $AB$ is $1$ and the length of $BC$ is $7$, then what is the circle's radius?

First step: Let $O$ be the centre of the circle.  Apply the law of sines to $\triangle OBA$ and $\triangle OBC$.
