Question

a1=10 r=5 Aflati suma primilor 100 de termeni

Answer 1

$a_{1} = 10$

$r = 5$

$a_{100}=a_{1}+(n-1)r$

$a_{100} = 10 + (100 - 1) \times 5$

$a_{100} = 10 + 99 \times 5$

$a_{100} = 10 + 495$

$a_{100} = 505$

$S_{100} = \frac{n(a_{1} + a_{100})}{2}$

$S_{100} = \frac{100(10 + 505)}{2}$

$S_{100} = \frac{100 \times 515}{2} = 50 \times 515 = 25750$

Formule :

$a_{n}=a_{1}+(n-1)r$

$S_{n} = \frac{n(a_{1} + a_{n})}{2}$