5.8 (7.9 - 2.8) + 5.1 = 29.58 + 5.1 = 34.68
2х - 10х -10 = 2х(в кв.) -10х - 5х +50
2х- 2х(в кв.) +5х = 50+10
-2х (в кв) + 7х = 60
- 5х = 60
х = 60: (-5)
х = - 12
3)
(4a - 3 - 4)(4a - 3 + 4) =
= (4a - 7)(4a + 1)
4)
(x + 2x - 1)(x - 2x + 1) =
= (3x - 1)( - x + 1) =
= - (3x - 1)(x - 1)
-21х-15=21х+69
-21х-21х=69+15
-42х=84
х=84:(-42)
х=-2
X + y = 2
2x^2 - xy = 65
Решение
y = 2 - x
2x^2 - x( 2 - x ) = 65
2x^2 - 2x + x^2 = 65
3x^2 - 2x - 65 = 0
D = 4 + 780 = 784 ; V784 = 28
x1 = ( 2 + 28 ) : 6 = 5
x2 = ( 2 - 28 ) : 6 = - 26/6 = - 13/3 = - 4 1/3
y = 2 - x
y1 = 2 - 5 = - 3
y2 = 2 - 4 1/3 = - 2 1/3
Ответ ( 5 ; - 3 ) ; ( - 4 1/3 ; - 2 1/3 )