Answer:
Step-by-step explanation:
eq. of any circle with center (h,k) and r=1 is
(x-h)²+(y-k)²=1²
points (-18,15) and (-20,15) lie on it.
(-18-h)²+(15-k)²=1
(15-k)²=1-(-18-h)²
and (-20-h)²+(15-k)²=1
(15-k)²=1-(-20-h)²
so 1-(-18-h)²=1-(-20-h)²
-(18+h)²=-(20+h)²
324+36h+h²=400+40h+h²
40h-36h=324-400
4h=-76
h=-19
(15-k)²=1-(-18-(-19))²=1-1=0
k=15
so center is (-19,15)
