Wyznacz a1, n oraz Sn wiedzac, ze r=-2 i an=17. Ciag arytmetyczny. SZYBKO!!!
r=-2
an=17
a1=?
an=a1+(n-1)*r
17=a1+(17-1)*(-2)
17=a1-34+2
17=a1-32
a1=49
Sn=a1+an/2 *n
Sn= 49+17/2 *17=56/2 *17= 476
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r=-2
an=17
a1=?
an=a1+(n-1)*r
17=a1+(17-1)*(-2)
17=a1-34+2
17=a1-32
a1=49
Sn=a1+an/2 *n
Sn= 49+17/2 *17=56/2 *17= 476