2а(3а-5b) - 3a(2a-b) = 2a*3a +2a*(-5b) - 3a*2a -3a*(-b)=
= 6a² - 10ab -6a² + 3ab = (6a² -6a²) + (-10ab + 3ab)=
= - 7ab
-12b(1/4 - a) - 6a(2b - 1/3) =
= - 12b/4 - 12b * (-a) - 6a*2b - 6a/(-3) =
= - 3b + 12ab - 12ab + 2a =
= - 3b + 2a =
= 2a - 3b
при а= - 0,7 ; b=2
2*(-0,7) - 3*2 = - 1,4 - 6 = - (1,4 + 6,0) = - 7,4
7 - 2x + 9 = 6 - x
- 2x + x = 6 - 9 - 7
- x = - 10
x = 10
2*6-b=24 2a-12=24
12-b=24 2a=24+12
b=24-12 2a=36
b=12 a=36÷2
a=18
( x^2 + 4x + 1)(x^2 + 4x + 5) = 0
x^2 + 4x + 1 = 0
D = b^2 - 4ac = 16 - 4 = 12
x1 = (- 4 + 2√3) / 2 = - 2(2 - √3) / 2 = √3 - 2
x2 = ( - 4 - 2√3) / 2 = - 2( 2 + √3) / 2 = - √3 - 2
x^2 + 4x + 5 = 0
D = b^2 - 4ac = 16 - 20 = - 4 - дискриминант отрицательный,значит,корней нет.
Ответ: x1 = √3 - 2, x2 = - √3 - 2.