Let the equation of plane passing through (1,1,1) is a(x−1)+b(y−1)+c(z−1)=0 . . . (i) It is also passing through (1,−1,−1). ∴‌‌a(0)+b(−2)+c(−2)‌=0 ‌ or ‌b+c‌=0 . . . (ii) Since, Eq. (i) is perpendicular to the plane ‌∴‌2x−y+z+5‌=0 ‌2a−b+c‌=0 . . . (iii) Since, Eqs. (ii) and (iii) are identical ∴‌‌‌