It is asking you to find the sum of k^2 - 1 from k=1 to k=4. Since that is only 4 numbers, calculating the sum by hand wouldn’t be that bad.
(1^2 - 1) + (2^2 - 1) + (3^2 - 1) + (4^2 - 1) = 26
The easier way to find the sum is to use a few simple formulas.
When we have a term that is just a constant c, the formula is c*n.
When we have a variable k, the formula is k*n*(n+1)/2.
When we have a squared variable, the formula is k*n*(n+1)*(2n+1)/6.
In this case, we have a squared variable k^2 and a constant of -1.
So plug in n=4 to the formulas:
4*5*9/6 - 1*4 = 26
The answer is 26
Answer:idk how to do this im in 7th grade
Answer:
The number of baseball card to begin with is 143
Step-by-step explanation:
Let The number of baseball cards = x
The number of sold baseball card = 60% of x
= 0.6 x
The number of left baseball card = x - 0.6 x = 0.4 x
The number of card gave away = 30 % of left cards
= 0.3 × 0.4 x = 0.12 x
The number of card left in his possession = 40
So, 0.6 x + 0.12 x + 40 = x
Or, 40 = x - 0.6 x - 0.12 x
Or, 40 = 0.28 x
∴ x =
= 142.85 ≈ 143
Hence The number of baseball card to begin with is 143 Answer
Hello, thanks for using Brainly!
First, our equation is:
x 
Our first step is to simplify.
When you simplify you get 3 1/8.
This is another way you can get it: (Multiply across. )

Enjoy your day.
Answer:
5 hours
Step-by-step explanation:
Our goal here is 3 F because 82+3=85
Ok so you start at 82. For example, you can do 0.6×1=0.6 (no)
0.6×2=1.2 (no)
0.6×3=1.8 (no)
0.6×4=2.4 (no)
0.6×5=3 (yes)
82°+3°=85°