Question

ma ajuta si pe mine cineva va rog.

Answer 1

$2 a_{10}= a_{5}+ a_{6}+36 \\ 2( a_{1}+9r)= a_{1}+4r+ a_{1}+5r+36 \\ 2 a_{1}+18r=2 a_{1}+9r+36 \\ 2 a_{1}+18r-2 a_{1}-9r=36 \\ 9r=36 \\ r=4$