Orthogonal circles (Circles x²+y²+2g₁x+2f₁y+c₁=0 and x²+y²+2g₂x+2f₂y+c₂=0 cut orthogonally)

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Circles x²+y²+2g₁x+2f₁y+c₁=0 and x²+y²+2g₂x+2f₂y+c₂=0 cut orthogonally iff 2g₁g₂+2f₁f₂=c₁+c₂.

What each symbol means

SymbolWhat it stands for
g_i,f_i,c_iCoefficients of respective circles

When to use this

Both circles written with unit coefficients on x² and y².