[tex] a_{4}- a_{2}=4
[/tex]\
[tex] a_{1}+ a_{3}+ a_{5}+ a_{6} =30 [/tex]
[tex] a_{1}+3r- a_{1}+r=4 [/tex] si [tex] a_{1}+ a_{1}+2r+ a_{1}+4r+ a_{1}+5r=30 [/tex]
din prima relatie 4r=4⇒r=1
inlocuim in relatia a doua si obtinem 4[tex] a_{1}+11=30 [/tex]
4a1=19⇒a1=19/4
