Răspuns :

Slavitescudoraid

f(1)=2-1=1

f(2)= 4-1=3

...........

f(10)=19

1+3+5+....+19

Aplic progresia aritmetica

a1=1

an=19

r=2

an= a1+(n-1)r

19= 1+(n-1)2

(n-1)2= 18

n-1=9

n=10

deci S19= (a1+an)×n /2 = (1+19)×10/2= 20×5=100

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