Question

Sa se determine primul termen al progresiei aritmetice a1,a2,19,25......

Answer 1

$a_{3} = 19$

$a_{4} = 25$

$a_{4} = a_{3} + r$

$r = a_{4} - a_{3} = 25 - 19 = 6$

$a_{3} = a_{2} + r$

$a_{2} = a_{3} - r = 19 - 6 = 13$

$a_{2} = a_{1} + r$

$a_{1} = a_{2} - r = 13 - 6 = 7$