Question

a15+a19=12
a17-?
kak reshit etu zadachu

Answer 1

Это арифметический прогрессия 
$a_{17} = frac{ a_{15} + a_{19} }{2} = frac{12}{2} =6$

Answer 2

spasibo bolshoe

Answer 3

ne za chto))

Answer 4

aveli chist xndrem))

Answer 5

hay es :D mersi shat shat :*

Answer 6

hay em, ba vonc))