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Question Number 17019 by tawa tawa last updated on 29/Jun/17

\underset{r = 1}{\sum^{3}} 2 r - 1 = ?

Answered by arnabpapu550@gmail.com last updated on 29/Jun/17

= (2 \times 1 - 1) + (2 \times 2 - 1) + (2 \times 3 - 1)

= 1 + 3 + 5 = 9

Commented by tawa tawa last updated on 29/Jun/17

God bless you sir .

Commented by arnabpapu550@gmail.com last updated on 30/Jun/17

For \underset{r = 1}{\sum^{30}} (2 r - 1)

= 1 + 3 + 5 + 7 + \cdot \cdot \cdot \cdot \cdot \cdot 30 terms .

= \frac{30}{2} [2 \times 1 + (30 - 1) \times 2]

= 30 \times (1 + 29) = 900