Question

calcule a soma dos 30 termos de pa (-3,-5,-7.....)

Answer 1

$a30 = a1 + 29r \\ a30 = - 3 + 29.( - 2) \\ a30 = - 3 - 58 \\ a30 = - 61 \\ \\ s30 = \frac{(a1 + an).n}{2} \\ s30 = \frac{( - 3 + ( - 61).30}{2} \\ s30 = \frac{( - 3 - 61).30}{2} \\ s30 = \frac{ (- 64).30}{2} \\ s30 = \frac{ -1920}{2} \\ s30 = - 960$