∠ B=β
∠ C= γ
В четырехугольнике NPMC
∠ PMC=90 °
∠ PNC=90 °
∠MPN=180 ° - γ
Аналогично
∠KPN=180 ° - α
∠KPM=180 ° - β
S_( Δ MNК)=S_( Δ KPM)+S_( Δ MPN)+S_( Δ KPN)=(1/2)*r^2*(sin (180 ° - α) +sin (180 ° - γ ) +sin(180 ° - β ) )=(1/2)*r^2(sin α +sin β +sin γ )
S_( Δ АВС)=S_( Δ AOB)+S_( Δ AOC)+S_( Δ BOC)=(1/2)*R^2*(sin ∠ AOB+sin ∠ AOC+sin ∠ BOC)=(1/2)*R^2(sin2 α +sin2 β +sin2 γ )=
=(1/2)*R^2* 2*(sin α cos α +sin β cos β +sin γ cos γ )
S_( Δ MNК)/S_( Δ АВС)=