The first term of an A.P. is 5 and the common difference is 4. Find the sum of first 12 terms of the A.P. and also 19th term.
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Step-by-step explanation:
Given that,
TThe first term of an A.P. = a = 5 and
Common difference = d = 4
Sum of first n termterms of an A.P.= Sn = n /2 [2a + ( n - 1 ) d ]
∴Sum of first 12 terms of an A. P.
S12 = 12/2 [ 2 × 5 + ( 12 - 1 ) 4 ]
= 6 [ 10 + ( 11 ) 4 ]
= 6 [ 10 + 44 ]
= 6 [ 54 ]
= 324 iis the answer.
∴19th term of an A. P.
a19 = a + 18 d
= 5 + 18 ( 4 )
= 5 + 72
= 77 is the answer.
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