Question

Numa PA de 12 termos, a soma do 1 termo com o ultimo é 10. Calcule a soma dos termos dessa PA

Answer 1

12+10+1=23 par de termo

Answer 2

$\mathrm{PA=\{a_1,a_2,a_3,\dots,a_{12}\}\ \ \|\ \ a_1+a_{12}=10}\\\\ \mathrm{S_n=\dfrac{(a_1+a_n).n}{2}\ \to\ S_{12}=\dfrac{(a_1+a_{12}).12}{2}}\\\\ \mathrm{S_{12}=(a_1+a_{12}).6\ \to\ S_{12}=10.6\ \to\ \boxed{\mathbf{S_{12}=60}}}$