Let equation of circle be x2+y2+2fx+2gy+c=0 The circle passes through (1,0) ‌1+0+2f+c=0 ‌c=−2f−1 The equation of circle becomes x2+y2+2fx+2gy−2f−1=0 The circle passes through (−1,1) 1+1−2f+2g−2f−1=0 4f−2g=1....(i) The circle also passes through (2,−1) ‌4+1+4f−2g−2f−1=0 ‌2f−2g=−4......(ii) Subtracting Eq. (ii) from Eq. (i), we get 2f‌=5 ⇒‌‌f=‌