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Mashcka [7]
3 years ago
8

-2,-7,-12 ,.... is an arithmetic sequence Find the sum of its first 20 terms ?​

Mathematics
1 answer:
nlexa [21]3 years ago
4 0

Given sequence:

-2,-7,-12 ,..

Unknown;

Find the sum of the first 20 terms = ?

Solution:

  The sequence is -2,-7,-12 ,..

To find he sum of n-terms of a sequence, we use the expression below;

     Sₙ  = \frac{n}{2} (2a + (n-1)d)

where n is the number of terms = 20

           a is the first term = -2

            d is the common difference= -7 - (-)2 = -5

Now input the parameters and solve;

       Sₙ  = \frac{20}{2} (2(-2) + (20 - 1) x -5)

      Sₙ = 10(-4 + -5(19))  = 10(-99)  = -990

The sum of the first 20 terms of the sequence is -990

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Could someone please explain! I cant figure it out.
qwelly [4]

2^-2 = 1/2^2

so: (1/2^2)*(12*3)-5^3

simplify: (1/4)*36-125

36*(1/4) = 36/4 so: 9-125

subtract: -116

3 0
3 years ago
michelle bought the same fabric on 3 different occasions and recorded the data below what was the price per yard of fabric? answ
bazaltina [42]

Please consider the complete question.

Michelle bought the same fabric on 3 different occasions and recorded the data below.

Yards of Fabric         Total Cost

2.2                             $2.53

3.6                             $4.14

4.2                             $4.83

What was the price per yard of fabric?

To find the cost per yard of fabric, we will divide cost of yards by number of yards.

\text{Cost per yard}=\frac{\text{Cost}}{\text{Number of yards}}

\text{Cost per yard}=\frac{\$2.53}{2.2\text{ yards}}

\text{Cost per yard}=\frac{\$1.15}{\text{ yard}}

Let us find cost per yard using 2nd set of data.

\text{Cost per yard}=\frac{\$4.14}{3.6\text{ yards}}

\text{Cost per yard}=\frac{\$1.15}{\text{ yard}}

Similarly we will find cost per yard for 3rd set of data.

\text{Cost per yard}=\frac{\$4.83}{4.2\text{ yards}}

\text{Cost per yard}=\frac{\$1.15}{\text{ yard}}

Therefore, the cost per yard of fabric is $1.15.

4 0
3 years ago
On a certain road map, the scale is 1 inch = 12 miles. Aurora Springs and Glendale are 4 inches apart on the map. What is the ac
AleksAgata [21]
Aurora Springs and Glendale are 48 miles apart. You would take how much one inch is and multiply it by 4 to get how much 4 inches is. so 12*4=48
6 0
3 years ago
MATH Simplify the expression -6w + (-8) + 1 + (-7w)
Luba_88 [7]

Answer: -13w - 7

Step-by-step explanation:

-6w + (-8) + 1 + (-7w)

Combine the like terms

-8 + 1 = -7

-6w + (-7) + (-7w)

-6w + (-7w) = -13w

-13w + (-7)

However, because adding a negative number is the same as subtracting the number as a positive, you can just make it -13w - 7

3 0
2 years ago
5.3: Solutions on a Number Line
andrew11 [14]

Answer:

idfk

Step-by-step explanation:

5 0
2 years ago
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