In A. P. 19 terms is 52 and 38 term is 128 ,find sum of first 56 terms
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Step-by-step explanation:
A(19) = 52
a + 18d = 52 -------(1)
A(38) = 128
a + 37d = 128 ------(2)
equation (1) - (2) से
19d = 76
d = 4
equation (1) से -
a + 72 = 52
a = -20
Sum of first 56 terms -
S(56) = 56/2 {2(-20)+(56-1)4}
= 28 {-40 + (55)4}
= 28{-40 + 220}
= 28 * 180
= 5040
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