Find the sum of first three terms of the following sequence whose $n^{t h}$ term is $5 n^{2} - 2$ .

68

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86

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69

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82

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Solution

The correct option is A $68$
Given, $T_{n} = 5 n^{2} - 2$
So, $T_{1} = 5 - 2 = 3$
$T_{2} = 5 (2^{2}) - 2 = 18$
$T_{3} = 5 (3^{2}) - 2 = 47$
So, Sum of first three terms $= 3 + 18 + 47 = 68$

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