Question

Qual o primeiro termo de uma pa da razao -5 onde o decimo termo e 12

Answer 1

$a_1=?\\ r=-5\\ a_{10}=10\\ n=12\\\\\\ a_n=a_1+(n-1)*r\\\\\\ 12=a_1+(10-1)*(-5)\to \\\\ 12=a_1+9*(-5)\to \\\\ 12=a_1+(-45)\to \\\\ 12+45=a_1\to\\\\ a_1=57$


PA(57, 52, 47, 42, 37, 32, 27, 22, 17, 12)