Dada la progresion - 6, - 3, 0, 3, 6 determine a_25 y S_30?

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<img src="https://tex.z-dn.net/?f=%5Ctext%7BT%5C%27ermino%20de%20lugar%2025%7D%20%5C%5C%5B2pt%5D%0Aa_%7B25%7D%3D3%2825%29-9%20%5C%5C%5B2pt%5D%0Aa_%7B25%7D%3D75-9%20%5C%5C%5B2pt%5D%0A%5Cboxed%7Ba_%7B25%7D%3D66%7D" />

<img src="https://tex.z-dn.net/?f=%5Cdisplaystyle%20%5Ctext%7BT%5C%27ermino%20de%20lugar%2030%7D%20%5C%5C%5B2pt%5D%20%0Aa_%7B30%7D%3D3%2830%29-9%3D90-9%3D81%20%5C%5C%5B4pt%5D%20%0AS_%7B30%7D%20%5Ctext%7B%20es%20la%20suma%20de%20los%2030%20primeros%20t%5C%27erminos%20de%20la%20progresi%5C%27on%7D%20%5C%5C%0A%5Ctext%7BSe%20usa%20la%20f%5C%27ormula%20%3A%7D%5C%5C%5B4pt%5D%20%0AS_n%3D%5Cleft%28%20%5Cfrac%7Ba_1%2Ba_n%7D%7B2%7D%5Cright%29n%20%5C%5C%5B4pt%5D%20%0A%5Ctext%7BEn%20el%20ejercicio%20%3A%20%7D%20%5C%5C%5B2pt%5D%20%0AS_%7B30%7D%3D%5Cleft%28%20%5Cfrac%7Ba_1%2Ba_%7B30%7D%7D%7B2%7D%5Cright%29%2830%29%20%5C%5C%5B4pt%5D%20%0AS_%7B30%7D%3D%5Cleft%28%20%5Cfrac%7B-6%2B81%7D%7B2%7D%5Cright%29%2830%29%3D%5Cleft%28%5Cfrac%7B75%7D%7B2%7D%5Cright%29%2830%29%3D1125%20%5C%20%5C%20%5Cleftarrow%20%5C%20Respuesta%5C%5C%5B4pt%5D%20%0A" />.