Odpowiedź:
Zadanie 4
a1 = 3 a4 = -15 a4 = a1 + 3r
-15 = 3 + 3r
-18 = 3r
r = -6
S6 = [tex]\frac{2a1+(n-1)r}{2} *n = \frac{6+6-1*(-6)}{2} * 6 = \frac{6-30}{2} *6 = -12 *6 = -72[/tex]
Zadanie 5
a1 = -8+x
a2 = 2x
a3 = 12x-10
a2 = [tex]\frac{a1+a3}{2}[/tex]
2x = [tex]\frac{-8+x+12x-10}{2} =\frac{13x-18}{2} /*2[/tex]
4x = 13x - 18
-9x = -18
x = 2
a1 = -8+2 = -6
a2 = 2◦2 = 4
a3 = 12◦2 - 10 = 24-10 = 14
