1) 5(х+у)^2-10ху
2)20су+2(с-5у)^2
3)6(p+2q)^2-24pq
4)4a(a-2)-(a-4)^2

1) 5(х+у)²-10ху=5(x²+2xy+y²)-10xy=5x²+10xy+5y²-10xy=5x²+5y²=5(x²+y²);2)20су+2(с-5у)²=20cy+2(c²-10cy+25y²)=20cy+2c²-20cy+50y²=2c²+50y²=2(c²+25y²);3)6(p+2q)²-24pq=6(p²+4pq+4q²)-24pq=6p²+24pq+24q²-24pq=6p²+24q²=6(p²+4q²);4)4a(a-2)-(a-4)²=4a²-8a-(a²-8a+16)=4a²-8a-a²+8a-16=3a²-16.