$S_{n} = \frac{n}{2} (4n + 20) \\ \\S _{n - 1} = \frac{(n - 1)}{2} (4n - 4 + 20) \\ \\ S _{n - 1} = \frac{(n - 1)}{2} (4n + 16) \\ \\S _{n - 1} = \frac{(n - 1)(4n + 16)}{2} \\ \\ { \boxed{S _{n - 1} = {2 {n}^{2} + 6n - 8}}} \\$

(b).

from general equation:

$S _{n - 1} = \frac{(n - 1)}{2} (4n + 16)$

first term is 4n

common difference:

$16 = \{(n - 1) - 1 \}d \\ 16 = (n - 2)d \\ d = \frac{16}{n - 2}$

8 0

3 years ago

The person who answes my question can u stay because i have more thankyou

castortr0y [4]

Answer:

c. 60 mins

Step-by-step explanation:

12 * 5 = 60

15 * 4 = 60

5 0

3 years ago

How many times can i write the number 6 on 7 cards

Eva8 [605]

Ummmmmmmmmm 7 i think that is the wright answer

5 0

3 years ago

What is 88/9in a fraction

vitfil [10]

I think 88/9 is a fraction if you looking for a mixed number it will be 9 7/9.

5 0

3 years ago

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