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

(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

PLZZZZ HEEEEEEELLLPPP MEEEEE!

lesantik [10]

Answer:

144 it is D

Step-by-step explanation:

8 0

2 years ago

Read 2 more answers

If the length of a rectangle is x-2 and its area is 2x3 – 8x2 + 2x+12, it’s width would be what?

hram777 [196]

Width would have to be a quadratic
Use long division to find the other factor of the cubic polynomial P (x).
P (x) factors in case it is reducible over R[x]
if it weren't then P (x) mod R [x] would be a field
otherwise you could use the Eisenstein Criterion.

6 0

3 years ago

1÷4=10 2÷8=20 4÷16=40 8÷16=?

Andre45 [30]

Answer is 80

How?
Sum multiplied by 2.

5 0

3 years ago