Question

4. Em Progressão Aritmética o segundo termo é 9, e o sétimo termo é 34. Dessa forma o primeiro termo dessa PA vale?

Answer 1

$a_n~=~a_m+(n-m)\cdot r\\\\\\\\a_7~=~a_2~+~(7-2)\cdot r\\\\\\34~=~9~+~5\cdot r\\\\\\r~=~\dfrac{34-9}{5}\\\\\\r~=~5\\\\\\\\a_1~=~a_2+(1-2)\cdot r\\\\\\a_1~=~9-r\\\\\\a_1~=~9-5\\\\\\a_1~=~4$