"Find a formula that describes the following function, which is composed of straight lines and a semicircle"

So far all I know is the equation has (x-1)(x+1), intersects at 1 and -1, but I don't get how the circle and straight lines kick in. Do I have to use some sort of hybrid between a straight line equation and the circle equation?

(x - h)2 + (y - k)2 = r2