X+y=2
x=2-y
x²y²-xy=12
xy(xy-1)=12
y(2-y)*(y(2-y)-1)-12=0
(2y-y²)((2y-y²)-1)-12=0
(2y-y²)=a
a(a-1)-12=0
a²-a-12=0
a1+a2=1 U a1*a2=-12
a1=-3⇒2y-y²=-3
y²-2y-3=0
y1+y2=2 U y1*y2=-3
y1=-1⇒x1=2+1=3
y2=3⇒x2=2-3=-1
a2=4⇒2y-y²=4
y²-2y+4=0
D=4-16=-12<0 нет решения
Ответ (3;-1);(-1;3)
a₁ = - 6,5 a₂ = - 6 Sₙ = - 42,5 n = ?
a₂ = a₁ + d
d = a₂ - a₁ = - 6 - (- 6,5) = - 6 + 6,5 = 0,5
![S_{n}=\frac{2a_{1}+d(n-1) }{2}*n\\\\-42,5=\frac{2*(-6,5)+0,5(n-1)}{2}*n\\\\(-13+0,5n-0,5)*n=-85\\\\0,5n^{2}-13,5n+85=0\\\\n^{2}-27n+170=0\\\\D=(-27)^{2}-4*170=729-680=49=7^{2}\\\\n_{1}=\frac{27+7}{2}=17\\\\n_{2}=\frac{27-7}{2}=10](https://tex.z-dn.net/?f=S_%7Bn%7D%3D%5Cfrac%7B2a_%7B1%7D%2Bd%28n-1%29%20%7D%7B2%7D%2An%5C%5C%5C%5C-42%2C5%3D%5Cfrac%7B2%2A%28-6%2C5%29%2B0%2C5%28n-1%29%7D%7B2%7D%2An%5C%5C%5C%5C%28-13%2B0%2C5n-0%2C5%29%2An%3D-85%5C%5C%5C%5C0%2C5n%5E%7B2%7D-13%2C5n%2B85%3D0%5C%5C%5C%5Cn%5E%7B2%7D-27n%2B170%3D0%5C%5C%5C%5CD%3D%28-27%29%5E%7B2%7D-4%2A170%3D729-680%3D49%3D7%5E%7B2%7D%5C%5C%5C%5Cn_%7B1%7D%3D%5Cfrac%7B27%2B7%7D%7B2%7D%3D17%5C%5C%5C%5Cn_%7B2%7D%3D%5Cfrac%7B27-7%7D%7B2%7D%3D10)
Ответ : 10 членов
1)-0.2*(-0.2)=0.04
2)0,04*10+17=0.4+17=17.4
1\33 так как в алфавите 33, а удовлетворяющее условие одно