[latex] a_{7}=-5; a_{37}=70; a_{1}=? d=? [/latex] Арифеметическая прогрессия

[latex] a_{37} = a_{7} +6d[/latex] 70=-5+30d 75=30d d=75/30=2.5 [latex] a_{1} = a_{7} - 6d[/latex] [latex] a_{1} [/latex]= -5-6*2.5 [latex] a_{1} [/latex]=-5-15 [latex] a_{1} [/latex]=-20