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find the sum of the first 21st term of the arithmetic sequence 3,10 17...​

Sagot :

Jadzpaglinawango

Answer:

a sum of 7 and 21st term is 143

Step-by-step explanation:

3,10,17,24,31,38,45,52,59,66,73,80,87,94,101,108,115,122,129,136,143.

Roldan1981go

Answer:

Solution:

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

[tex]S_{21}[/tex]  = [tex]\frac{21}{2} (2(3)+ (21-1)7)[/tex]

       = 10.5 (6+20)7

        = 10.5(26)7

        = 10.5(182)

        = 19110

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