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

(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

2 years ago

Simplify the expression: 2(4x-3)-7(x+1)

Aliun [14]

2(4x-3)-7(x+1) first distribute
8x-6-7x+7 then combine the x's
<u>x+13 </u>

4 0

3 years ago

Find the distance between the following coordinates: I(-a,b), J(a,b)

olchik [2.2K]

Answer:

Step-by-step explanation:

using distance formula:

√(x₂-x₁)² + (y₂-y₁)²

putting values,

√{a-(a)}² + {b-b}² = √ {a+a}² + 0²

= √(2a)² = √4a² = 2a

Hope this helps:)

8 0

2 years ago

HELP PLZZZZ like asap

Anestetic [448]

Answer:

The answer is B

Step-by-step explanation:

✌

7 0

2 years ago

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