Question

Which term of the AP -2,-7,-12,......, will be -77? Find the sum of this AP up to the -77.​
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Answer 1

Answer:

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Step-by-step explanation:

Given :

The A.P is -2,-7,-12,.........

The first term,a => -2

The common difference, d => t2-t1

=> -7- (-2)

=> -7 + 2

d => -5

Solution:

The nth term of an A.P,

tn = a + (n-1) d

-77= -2 + (n-1) -5

-77= -2 -5n +5

-77= -5n +3

5n = 3+77

5n = 80

n = 16

The 16th term of this A.P is -77

Sum of the terms of an A.P = n/2 (a+l)

l => The last term of the A.P

n => Number of terms

a => The first term of an A.P

Sum of the terms of an A.P upto -77 is

=> 16/2 (-2 +(-77))

=> 8 ( -79)

=>632

The sum of terms of an A.P upto -77 is -632..

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