given that the first term of an a. p is7 and the 10th term is twice
the 2nd term. calculate the 19th term and the sum of the
28 term
Tn = a + (n-1) d
T1 = a + ( 0 ) d = a = 7
so
Tn = 7 + (n-1) d
T10 = 7 + 9 d = 2 * [ 7 + d ]
7 + 9 d = 14 + 2 d
7 d = 7
d = 1
so Tn = 7 + (n-1)1 = 6 + n
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