2-0.3(b3a)=2-0.3(0.6+3*(-0.2))
2-0.3(0.6-0.6)=0
Ответ:0
21, 18, 15, 12, 9, 6, 3, 0
<span>Ответ: 0</span>
S13= (2a<span>1 </span>+ 12d) * 13 /2 = 130a4, a10, a7 - последовательные члены геометрической прогрессии.а4*а7 = а102<span>(a1+3d)(a1+6d) = (a1+9d)2</span><span>а12 +9а1*d +18d2 = a12 +18a1*d +81d2</span><span>Упростив, получим а1 = -7d (1)
</span><span>S13 = (a1+6d)*13 = 130</span><span>a1+6d = 10 (2)</span>Решим систему (1),(2).a1=70, d = -10
7x-12=27x+24-2x
7x-12=25x+24
18x=-12-24
18x=-36
x=-2
Ответ: x=-2