Question

find sum of series 7+12+17+....upto30 terms
6+15+24+....+105



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Answer 1

Answer:

a=7,d=12-7=5

$\binom{105}{2} {2a + (n - 1)d = \binom{105}{2} {2 \times 7(105 - 1)5 = \binom{105}{2} {14 +104 \times 5} = \binom{105}{2} {14 + 109} = \binom{105}{2} \times (123) = 105 \times 116 = 12180$

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