Question

Determinanti ratia progresiei aritmetice a1+a2+a3+a4=14 si a1=2

Answer 1

$a_{1}$=2
$a_{2}$=3
$a_{3}$=4
$a_{4}$=5
S=$\frac{ {n} ( a_{n}+ a_{1} ) }{2} = \frac{ {n} ( a_{4}+ a_{1} ) }{2} =\frac{ 4 ( 5+2) }{2} =\frac{ {4} x7 }{2} = \frac{28}{2} =14$
$r= a_{n} - a_{n-1} =5-4=1$

r=1

Answer 2

a2=a1+r
a3=a1+2r
a4=a1+3r
a1+a1+r+a1+2r+a1+3r=14
4*2+6r=14
8+6r=14
6r=6
r=1