Сестра - x
Брат - y
Составим систему уравнении
![\left \{ {{x-y=6} \atop {2y=x-1}} \right.](https://tex.z-dn.net/?f=+%5Cleft+%5C%7B+%7B%7Bx-y%3D6%7D+%5Catop+%7B2y%3Dx-1%7D%7D+%5Cright.+)
![\left \{ {{x=6+y} \atop {2y-y=5}} \right.](https://tex.z-dn.net/?f=+%5Cleft+%5C%7B+%7B%7Bx%3D6%2By%7D+%5Catop+%7B2y-y%3D5%7D%7D+%5Cright.+)
![\left \{ {{y=5} \atop {x=11}} \right.](https://tex.z-dn.net/?f=+%5Cleft+%5C%7B+%7B%7By%3D5%7D+%5Catop+%7Bx%3D11%7D%7D+%5Cright.+)
Сестре 11 лет, брату 5 лет.
.
(-8/7)• ((4/5)+(19/20))•((36+5)/6 +(12+2)/3)= (-8/7)•((16/20)+(19/20))• (41/6 +14/3)=(-8/7)•(7/4)•((41+28)/6)=(-2)• (69/6)=-69/3=-23
1) xy²-x+5-5y²=y²(x-5)-(x-5)=(x-5)(y²-1)=(x-5)(y-1)(y+1)
2)m^5(m³+3³)=m^5(m+3)(m²+3m+9)
X=(z/3)-y
y=(z/3)-x
Как-то так