Question

S10=8S2
S3=-3
Cat este S10,S2, primul termen si ratia?
DAU CORONITA

Answer 1

S10= a1+a2+..+a10 = a1+a1+r+...+a1+9r = 10a1+45r
S2= a1+a2 = a1+a1+r = 2a1+r
S3= a1+a2+a3 = a1+a1+r+a1+2 = 3a1+3r
S3= 3a1+3r= -3 =>  a1+r= -1
S10 = 8S2 => 10a1+45r = 16a1+8r => 6a1=37r
a1+r = -1|x6
6a1+6r = -6
6a1 = 37r => 37r+6r = -6 => 43r = -6 => r = -6/43
=>a1= -1-r= -1+6/43= -37/43=a1
S10= 10a1+45r= -370/43-270/43= -640/43
S2=2a1+r = -74/43-6/43= -80/43
aceasta e problema. a dat cam aiurea dar sper sa fie bine. verifici tu la calcule