Question

Find the sum of first 10 terms of the sequence {an }where an=5-6n, where n is a natural number

Answer 1

Answer:

-280

Step-by-step explanation:

an = 5 - 6n

Find the 1st term:

a1 = 5 - 6(1)

a1 = -1

Find the 10th term:

a10 = 5 - 6(10)

a10 = -55

Find the sum of the 10 terms:

sn = n/2 (a1 + an)

s10 = 10/2 (-1 + (-55)) = -280

Answer: The sum is -280

Answer 2

Answer:

Step-by-step explanation:

Hi ,

an = 5 - 6n

1 ) a1 = 5 - 6= -1

2 ) a2 = 5 - 12 = -7

3 ) a3 = 5 - 18 = -13

d = a2 - a1

d = -7 - ( -1 ) = -7 +1 = -6

now ,

a = - 1 , d = -6

sum of n terms = n/2 [ 2a + ( n - 1 ) d]

Sn = n/2[ 2×(-1 ) + ( n -1 )(-6) ]

Sn = n/2 [ -2 -6n + 6 ]

= n/2 [4 - 6n ]

= n(2-3n )

I hope this helps you.

:)

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