А10=а1+9d
a8=a1+7d
a5=a1+4d
a1+a10=a1+a1+9d=2a1+9d=12
a8-a5=a1+7d-a1-4d=3d=4 --> d= 4/3
2*a1+9* 4/3= 2*a1 +12= 12 --> a1=0
D= 9-5=4
230=(2*5+4n-4)*n)/2
460=10n+4n^2-4n
4n^2+6n-460=0
D=1849
X1=11.5
X2=10
<span>ответ:10</span>
(y-6)(y+6)/3y(y-6)=y+6/3y
-4+6/-12=-2/-12=1/6