An=a1+d(n-1)
a21=a1+20d
a39=a1+38d
Cоставим систему:
33=a1+20d
36.6=a1+38d
Отнимем из первого уравнения второе:
33-36.6=a1-a1+20d-38d
-3.6=-18d<u />
d=0.2
Найдём теперь a1 :
33=a1+20*0.2
33=a1+4
a1=33-4
a1=29
Найдём a6 :
a6=a1+5d
a6=29+5*0.2=29+1=30
S6=(a1+a6)/2*6=(a1+a6)*3=(29+30)*3=177
3) (m⁻⁴/(10n⁵k²))⁻² : (5m²n³k)³ = (10n⁵k²/m⁻⁴)² · (5m²n³k)⁻³
= 10² · n¹⁰k⁴m⁸ · 5⁻³ · m⁻⁶n⁻⁹k⁻³ = 100/125 · m⁽⁸⁻⁶⁾n⁽¹⁰⁻⁹⁾k⁽⁴⁻³⁾ = 4m²nk/5
4) (9c⁵/(a³b⁻²))⁻² : (a²b⁻³/(6c⁴))³ = (a³b⁻²/(9c⁵))² · (6c⁴/(a²b⁻³))³ =
= (a⁶b⁻⁹/(9²c¹⁰)) · (6³c¹²/(a⁶b⁻⁹)) = 1/81 · a⁶b⁻⁹c⁻¹⁰ · 216c¹²a⁻⁶b⁹ = 8/3 · a⁽⁶⁻⁶⁾b⁽⁹⁻⁹⁾c⁽¹²⁻¹⁰⁾ = 8c²/3
3√80-2√20-√180=3√(4*20)-2√20-√(9*20)=3*2√20 - 2√20 - 3√20 = 6√20 - 2√20 - 3√20 = √20*(6-2-3) = √20
(2/5+3,2)÷4/9=(0,4+3,2)÷4/9=3,6÷4/9=3 6/10÷4/9=36/10÷4/9=81/10=8,1