x²+y²-10x+74+14у-(x-5)² = x²+y²-10x+74+14у-(x²-10х+25)=
=x²+y²-10x+74+14у-x²+10х-25=у²-10х+14у+49=
=(у²+14у+49)-10х=(у+7)²-10х
x²+y²-10x+74+14у-(x-5)² = x²+y²-10x+74+14у-(x²-10х+25)=
=x²+y²-10x+74+14у-x²+10х-25=у²-10х+14у+49=
=(у²+14у+49)-10х=(у+7)²-10х