{20^{th}} term of series 2 × 4 + 4 × 6 + 6 × 8 + ....... will be

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8. Sequences and Series

easy

The ${20^{th}}$ term of the series $2 \times 4 + 4 \times 6 + 6 \times 8 + .......$ will be

A

$1600$

B

$1680$

C

$420$

D

$840$

Solution

(b) The given series $2 \times 4 + 4 \times 6 + 6 \times 8….$

${n^{th}}$ terms${T_n} = 2n\;.\;2(n + 1) = 4n(n + 1)$

Putting $n = 20$,

we get ${T_{20}} = 4\;.\;20(20 + 1) = 1680$.

Standard 11

Mathematics

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