1) (a2-b2)-(a2-b2)=a2-b2-a2+b2=0
2) 3a2-a(a-b)=3a2-a2+ab=3+ab
2*5*14=140
25*4*7=700
4*5*5*8=800
2*5*70=700
50*2*3=300
8*9*2*5=720
(570+330):3-х:5=100
900:3-х:5=100
300-х:5=100
х:5=300-100
х:5=200
х=200·5
х=1000
(570+330):3-1000:5=100
1. х/7=21
х=21/7
х=3
2. - 10*х=-30
х=-30/(-10)
х=3
3. х-40=-37
х=40-37
х=3