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riadik2000 [5.3K]
3 years ago
15

In an arithmetic series, the sum of the first 12 terms is equal to ten times the sum of the first 3 terms. If the first term is

5, find the common difference and the value of S20.
Mathematics
1 answer:
arlik [135]3 years ago
8 0

Answer:

Step-by-step explanation:

The formula for determining the sum of the first n terms of an arithmetic sequence is expressed as

Sn = n/2[2a + (n - 1)d]

Where

n represents the number of terms in the arithmetic sequence.

d represents the common difference of the terms in the arithmetic sequence.

a represents the first term of the arithmetic sequence.

If a = 5, the expression for the sum of the first 12 terms is

S12 = 12/2[2 × 5 + (12 - 1)d]

S12 = 6[10 + 11d]

S12 = 60 + 66d

Also, the expression for the sum of the first 3 terms is

S3 = 3/2[2 × 5 + (3 - 1)d]

S3 = 1.5[10 + 2d]

S3 = 15 + 3d

The sum of the first 12 terms is equal to ten times the sum of the first 3 terms. Therefore,

60 + 66d = 10(15 + 3d)

60 + 66d = 150 + 30d

66d + 30d = 150 - 60

36d = 90

d = 90/36

d = 2.5

For S20,

S20 = 20/2[2 × 5 + (20 - 1)2.5]

S20 = 10[10 + 47.5)

S20 = 10 × 57.5 = 575

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As the assumption quadrilateral ABCD is shown in figure a.  

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<u>So,option (B) is true</u> <u>i.e segment</u><u> </u><u>B'D' will run through (2,2) and will be longer than the segment BD.</u>

<u />

Learn more about dilation from brainly.com/question/12528454

#learnwithBrainly

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