Question

qtos termos teem a p.a. 3,7,11...,99)?

Answer 1

$p.a.( 3,7,11...,99)\\\\\\ a_1=3\\ a_n=99\\ r=7-3=4\\ n=?\\\\\\ a_n=a_1+9n-1)*r\\\\\\ 99=3+(n-1)*4\to \\\\ 99=3+4n-4\to \\\\ 99-3+4=4n\to \\\\ 100=4n\to \\\\ \frac{100}{4} =n\to \\\\ n=25$