Question

Find the sum of the first 20 terms of the arithmetic sequence 15,19,23,27,

Answer 1

Héyå

Sølûtíoñ=> a = 15, d=19-15=4, n=20

we know that:

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

S=20/2[2(15)+(20-1)4]

S=10[30+76]

S=1060

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Answer 2

Answer:

sum of the first 20 terms in arithmetic sequence=15,19,23,27,3,... is 1060.

Step-by-step explanation:

Am=15,19,23,27,3,...

here

first term a =15

d=a2-a1=19-15=4

and total number of the terms of which sum should be obtained n=20

formula to find sum of the first 20 numbers of an arithmetic sequence is

$Sn= \frac{n}{2} (2a + (n - 1)d)$

$Sn= \frac{20}{2} (2 \times 15 + (20 - 1) \times 4) \\ = 10 \times 30 + (19) \times 4) \\ = 10 \times (30 + 76) \\ = 1060.$

therefore sum of first 20 term of Am=15,19,23,27,3,...is 1060.#SPJ3 .