Ответ:
(1.6*10^(-5))*(4*10^7)= 6.4*10^7*4*10^(-5)*10^2=25.6*10^4
x+x+19=41
2x=41-19
2x=22x
x=11
x+19=11+19=30
Ответ: на первое полке 11 книг,на второй 30
3а*-5ь*-2с=-30аьс
-25а*0.04с=-ас
-5 ; -3 ; -1 ; 1 ; 3 ; 5 ; 7 ; 9 ; 11
Ответ: 11
![\left \{ {{x-3y=8\, |\cdot (-2)} \atop {2x-y=6\qquad \; }} \right. \plus \left \{ {{x-3y=8} \atop {5y=-10}} \right. \; \; \left \{ {{x=3y+8} \atop {y=-2}} \right. \; \; \left \{ {{x=2} \atop {y=-2}} \right. \quad \Rightarrow \; \; (2,-2)](https://tex.z-dn.net/?f=+%5Cleft+%5C%7B+%7B%7Bx-3y%3D8%5C%2C+%7C%5Ccdot+%28-2%29%7D+%5Catop+%7B2x-y%3D6%5Cqquad+%5C%3B+%7D%7D+%5Cright.+%5Cplus+++%5Cleft+%5C%7B+%7B%7Bx-3y%3D8%7D+%5Catop+%7B5y%3D-10%7D%7D+%5Cright.+%5C%3B+%5C%3B++%5Cleft+%5C%7B+%7B%7Bx%3D3y%2B8%7D+%5Catop+%7By%3D-2%7D%7D+%5Cright.+%5C%3B+%5C%3B++%5Cleft+%5C%7B+%7B%7Bx%3D2%7D+%5Catop+%7By%3D-2%7D%7D+%5Cright.+%5Cquad+%5CRightarrow+%5C%3B+%5C%3B+%282%2C-2%29)
x=2>0 , y= -2<0 ⇒ точка находится в 4 четверти