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3 years ago

I NEED HELP PLEASE THANKS! :) Find the seventh partial sum of 13, 22, 31, 40, ...

Mathematics

2 answers:

Harrizon [31]3 years ago

7 0

Answer:

Step-by-step explanation:

Arithmetic sequence

First term a = 13

Common difference = 2nd term - first term

= 22 - 13

d = 9

$a_{n}= a + (n-1)d\\\\a_{7}= 13 + 6*9$

= 13 + 54

= 67

Sum of 7 terms = $\frac{n}{2}(2a + (n-1)d)\\\\$

= $\frac{7}{2}(2*13+6*9)\\$

= $\frac{7}{2}(26+54)\\$

= $\frac{7}{2}*80\\$

= 7 *40

= 280

Olin [163]3 years ago

5 0

Answer:

280

Step-by-step explanation:

the 7th number is

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