Question

16+19+22+25+...+661=54x
x= ??? Va rog.Dau coroana.

Answer 1

16+19+22+25+...+661=54x
Sirul este in progresie aritmetica.

a₁=16
r=3

Formula termenului general : $a _{n} =a_{1} +(n+1)*r$
 
$S_{n}= \frac{(a_{1}+a_{n})*n}{2}$

a$_{n}$ = 661 

661= 16 + (n+1) *3 => 661= 16 + 3n+3 => 661 = 19 +3n => 642= 3n => n= 214

$S_{n}= \frac{(16+661)*214}{2} = \frac{144878}{2} =72439$

54x= 72439

x=$\frac{72439}{54}$