1) 5 (х+у) ^2-10 ху

2) 20 су+2 (с-5 у) ^2

3) 6 (p+2q) ^2-24pq

4) 4a (a-2) - (a-4) ^2

1) 5 (х+у) ²-10 ху=5 (x²+2xy+y²) - 10xy=5x²+10xy+5y²-10xy = 5x²+5y²=5 (x²+y²) ;

2) 20 су+2 (с-5 у) 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.