Uite partea teoretica a rezolvarii tale:
-formula termenului general: aₙ=a₁+(n-1)r
a₅=12
a₁+a₄=9
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a₁=?;
r=?
a₅=a₁+(5-1)r=a₁+4r => a₁+4r=12
a₄=a₁+(4-1)r=a₁+3r
a₁+a₄=9 => a₁+a₁+3r=9 +> 2a₁+3r=9
2a₁+3r=9
a₁+4r=12
------------- Scadem
2a₁+3r-a₁-4r=9-13
a₁-r=-3 => a₁=r-3
a₁+4r=12 => r-3+4r=12 => 5r=12+3=15 => r=15/5 => r=3
a₁=r-3 => a₁=3-3 => a₁=0
Raspuns: a₁=0; r=3
