Question

determine a1 de um PA e a razão é - 2 e o a22=-200​

Answer 1

Podemos utilizar o termo geral da PA, acompanhe:

$\sf a_n~=~a_1~+~(n-1)\cdot r\\\\\\a_{22}~=~a_1~+~(22-1)\cdot r\\\\\\-200~=~a_1~+~21\cdot (-2)\\\\\\-200~=~a_1~-~42\\\\\\a_1~=\,-200~+~42\\\\\\\boxed{\sf a_1~=\,-158}$

$\Huge{\begin{array}{c}\Delta \tt{\!\!\!\!\!\!\,\,o}\!\!\!\!\!\!\!\!\:\,\perp\end{array}}Qualquer~d\acute{u}vida,~deixe~ um~coment\acute{a}rio$