[tex] > resolucao \\ \\ \\ \geqslant progressao \: aritmetica \\ \\ \\ r = a2 - a1 \\ r = - 9 - ( - 7) \\ r = - 9 + 7 \\ r = - 2 \\ \\ \\ an = a1 + (n - 1)r \\ an = - 7 + (28- 1) - 2 \\ an = - 7 + 27 \times ( - 2) \\ an = - 7 + ( - 54) \\ an = - 7 - 54 \\ an = - 61 \\ \\ \\ \\ \geqslant a \: soma \: dos \: termos \: da \: pa \\ \\ \\ sn = \frac{(a1 + an)n}{2} \\ \\ sn = \frac{( - 7 + ( - 61)28}{2} \\ \\ sn = \frac{( - 7 - 61)28}{2} \\ \\ sn = \frac{ - 68 \times 28}{2} \\ \\ sn = - 68 \times 14 \\ \\ sn = - 952 \\ \\ \\ \\ = = = = = = = = [/tex]
