Hello, geton!
Draw chord
Since is inscribed in a semicircle,
In right triangle
In right triangle
Hence: .
. . Therefore: .
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
In right triangle , we have:
. . .[1]
Since , part (a) gives us: .
Then we have: .
. . which simplifies to: .
. . which factors: .
And we have: . .**
Substitute into [1]: .
**
The other factor produces: .
. . which has no real root.