Respuesta :

meerkat18

First you have to find the 20th term... an = a1 + (n - 1)d n = 20 a1 = 8 d = 8 now lets sub... a20 = 8 + (20 - 1) * 8 a20 = 8 + 19 * 8 a20 = 8 + 152 a20 = 160 s20 is the sum of all the number till 20. so we will use the sum formula... sn = n(a1 + an) / 2 s20 = 20 (8 + 160) / 2 s20 = 20 (168) / 2 s20 = 3360/2 s20 = 1680 any questions ?

Answer:

[tex]S_{20} =1680[/tex].

Step-by-step explanation:

Given : 8 + 16 + 24 + 32 +…..

To find : Find S20

Solution : We have given 8 + 16 + 24 + 32 +…..

First term = 8.

Common difference = 16 - 8= 8

                                     24 -16 = 8.

Sum of n term ( [tex]S_{n} =\frac{n}{2}[2 a+(n-1)d][/tex].

Where, a = first term ,  d =common difference .

For n = 20 , a = 8 , d = 8

[tex]S_{20} =\frac{20}{2}[2*8+(20-1) 8][/tex].

[tex]S_{20} =10[16+(19) 8][/tex].

[tex]S_{20} =10[16+152][/tex].

[tex]S_{20} =10[168][/tex].

[tex]S_{20} =1680[/tex].

Therefore,4) [tex]S_{20} =1680[/tex].

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