Question

.................. dau coroană ......... ......​

Answer 1

Răspuns:

Explicație pas cu pas:

a₈=a₁+7r=40

a₂₀=a₁+19r=-20

12r=-60

r=-5⇒a₁=75

a₇=a₁+6r=75-30=45

a₅₂=-125

r=-5

a₅₂=a₁+51r=-125

a₁-255=-125

a₁=130

a₂=3=a₁+r⇒$a_{1}=3-\frac{2}{3}=\frac{7}{3}$

a₅=5=a₁+4r

3r=2

r=$\frac{2}{3}$

a₂₈=a₁+27r=$\frac{7}{3} +\frac{54}{3} =\frac{61}{3}$

$S_{28}=\frac{(a_{1}+a_{28})\cdot28}{2}=\frac{(\frac{7}{3}+\frac{61}{3} ) }{2}=\frac{34}{3}$