A1=12 d=5 an=97
a1+5(n-1)=an
12+5(n-1)=97
5(n-1)=85
n-1=17
n=18
S18=(a1+a18)*18/2=(12+97)*9=109*9=981
1) (a^5)^3 × a = a^16
3) ((a^3)^2)^4=a^24
А) 8ab-6ac=2a(4b-3c)
б) 0.16-c² =(0.4-c)(0.4+c)
9b(b-1)-(3b+2)² =9b²-9b -(9b²+12b+4)=9b²-9b-9b²-12b-4=-21b-4
{x+4y=7
{x-2y=-5
x=7-4y
7-4y-2y=-5
7-6y=-5
-6y=-5-7
-6y=-12
y=2
x=7-4*2=7-8=-1
Ответ: х=-1
у=2
1)(1/2)⁻⁷-75·5⁻²=2⁷-75/25=128-3=125;
2)(2/3)⁻⁴·32-(0.2)⁻³=(3/2)⁴·2⁵-(1/0.2)³=3⁴·2-5³=162-125=37;
3)25²·(-5)⁻⁵+1.2·(1/6)⁻²=5⁴·(-5)⁻⁵+1.2·6²=(-5)⁴⁻⁵ +0.2·6·6²=(-5)⁻¹+0.2·6³=
=(-1/5)+0.2·216=-0.2+43.2=43
4)(-1²/₃)³·(1/3)⁻⁴-0.8·2⁻³=(-5/3)³·3⁴-8·0.1·2⁻³=(-5)³·3⁴⁻³-2³⁻³·0.1=
=(-5)³·3-0.1=(-375)-0.1=-375.1