3х - 5у = - 18
- 2х + 7у = 36
Решение
2х = 7у - 36
Х = 3,5у - 18
3( 3,5у - 18 ) - 5у = - 18
10,5у - 54 - 5у = - 18
5,5у = - 18 + 54
у = 36 : 5,5
у = 36 : ( 11/2 ) = 72/11 = 6 6/11
Х = 7/2 • 72/11 - 18 = ( 252/11 ) - 18 = 22 10/11 - 18 = 4 10/11
Ответ ( 4 10/11 ; 6 6/11 )
{6x-3≥3
{-5x≤-10
6x-3≥3
6x≥3+3
6x≥6
x≥6 : 6
х≥1
-5х≤-10
х≥ -10 : (-5)
х≥2
\\\\\\\\\\\\\\\\\\\\\\\\\\
--------- 1 --------- 2 ----------
\\\\\\\\\\\\\\\
x≥2 или х∈[2; +∞)
A25=a1+24d=-2+24*5=118 , an=a1-(n-1)*d