А8 = а1 + 7d
a18 = a1 + 17d
a8 - a18 = a1 - a1 + 7d - 17d
a8 - a18 = -10d
-24,1 + 39,1 = -10d
15 = -10d
d = -1,5
2+в-2ав-ав-(2-2в+а-ав)=2+в-2а-ав-2+8в+а+ав=3в-3а
=44(44-45)= 44*-1=-45
2) =81(19+1)=81*20=1620
(y-4)(y+4)-(y-3)^2=y^2-16 - y^2 +6y - 9=6y-25