Question

a1=6 r=3 a10=? S6=?​

Answer 1

Explicație pas cu pas:

$a_n=a_1+(n-1)r$

$a_{10}=6+9\cdot 3 =33$

$S_n = \dfrac{n}{2}\cdot (a_1+a_6)$

$S_6 = 3\cdot (6+6+5\cdot 3)= 81$ $\hfill{\boxdot}$

Answer 2

an=a1+r(n-1)

a10=a1+r(10-1)

a10=a1+9r

a10=6+9*3

a10=6+27

a10=33

S6=(a1+a6)*n/2

a6=a1+r(6-1)

a6=a1+5r

a6=6+5*3

a6=21

S6=(6+21)*6/2

S6=27*3

S6=81