1) 1000;2)720;3)5200;4)840;5)224,96;6)399,99;7)15,999... 8) 899,96; 9)7200; 10) 95040; 11)25,5; 12) -5,312..
X-2/5 = 2/3 - 3x - 2/6
x + 3x = 2/3 - 2/6 + 2/5
4x = (2*10 - 2*5 + 2*6)/30
4x = (20 - 10 + 12)/ 30
4x = 22/30
x = 22/30 : 4
x = 22/30 * 1/4
x = 11/60
Х^2-4х+8=40
х^2-4х+8-40=0
х^2-4х-32=0
Д=16+128=144=12^2
х1=4+12/2=8
х2=4-12/2=-4
х1+х2=8+(-4)=4