Zad 1: a7=243 q=-3 , oblicz a1
Zad 2: a1=2 q=1/3 , oblicz s4
Zad.1
a7 = 243
q = -3
a1 = ?
a7 = a1*q^6
a1 = a7/q^6 = 243/(-3)^6 = 243/729
a1 = 1/3
========
Zad.2
a1 = 2
q = 1/3
S4 = ?
Sn = [a1(1-q^n)]/(1-q)
S4 = {2[1-(1/3)^4}/(1-1/3) = 2(1-1/81)/(1-1/3) = 160/81:2/3 = 80/27
S4 = 2 26/27
===========
z.1
q = - 3
--------------
Mamy
czyli
243 = a1*(-3)^6
243 = a1*729
a1 = 243/729 = 1/3
=======================
z.2
-----------------
S4 = a1*[ 1 - q^4]/[1 - q]
S4 = 2*[1 - (1/3)^4]/[1 - 1/3]
S4 = 2*[1 - 1/81]/(2/3)
S4 = 3*( 80/81) = 240/81
S4 = 80/27
==========
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Zad.1
a7 = 243
q = -3
a1 = ?
a7 = a1*q^6
a1 = a7/q^6 = 243/(-3)^6 = 243/729
a1 = 1/3
========
Zad.2
a1 = 2
q = 1/3
S4 = ?
Sn = [a1(1-q^n)]/(1-q)
S4 = {2[1-(1/3)^4}/(1-1/3) = 2(1-1/81)/(1-1/3) = 160/81:2/3 = 80/27
S4 = 2 26/27
===========
z.1
a7 = 243
q = - 3
--------------
a1 = ?
Mamy
a7 = a1*q^6
czyli
243 = a1*(-3)^6
243 = a1*729
a1 = 243/729 = 1/3
=======================
z.2
a1 = 2
q = 1/3
-----------------
S4 = ?
S4 = a1*[ 1 - q^4]/[1 - q]
S4 = 2*[1 - (1/3)^4]/[1 - 1/3]
S4 = 2*[1 - 1/81]/(2/3)
S4 = 3*( 80/81) = 240/81
S4 = 80/27
==========