1) 12-2x-6=26
-2x=20
x=-10
2) -4z+6=z+7,2
-5z=1,2
z=0,24
3) 12x-24=3x-6
9x=18
x=2
<span>(a+1)^2+3(a-1)^2-5(a+1)(a-1)
(а^2+2a+1)+(3a^2-6a+6)+(-5a^2+5)
-a^2-4a+12
Ответ: -а^2-4a+12</span>
<span><span>(a+b)^3+(a-b)^3 / (<span>2ab(a^2+3b^2)</span>) - 1 =</span></span>
<span>=( a^3+3a^2b+3ab^2+b^3 + a^3-3a^2b+3ab^2-b^3) /(2ab(a^2+3b^2)) - 1 =</span>
<span>=(2a^3+6ab^2) /(2ab(a^2+3b^2)) -(2ab(a^2+3b^2)) /(2ab(a^2+3b^2)) =</span>
<span>=(2a(a^2+3b^2) -2ab(a^2+3b^2)) /(2ab(a^2+3b^2)) =</span>
<span>=(2a-2ab)(a^2+3b^2) /(2ab(a^2+3b^2)) = (2a-2ab) /(2ab)=2a(1-b)/(2ab)=</span>
<span>= (1-b) / b</span>
0,2 х²-0,2х - 0,2х²-0,5х -0,6х<-4