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Question Number 119107 by I want to learn more last updated on 22/Oct/20

Answered by 1549442205PVT last updated on 22/Oct/20

$$\mathrm{S}=1+3-5+7+9-11+13+15-17+19+21-23+...$$$$\mathrm{S}=(1+3-5)+(7+9-11)+(13+15-17)+(19+21-23)+$$$$(25+27-29)+...+[6\mathrm{n}-5+6\mathrm{n}-3-(6\mathrm{n}-5)]$$$$=-1+5+11+17+23+...+...+(6\mathrm{n}-7)$$$$=\frac{(-1+6\mathrm{n}-7)\mathrm{n}}{2}={3\mathrm{n}}^2-4\mathrm{n}$$$$\mathrm{S}={3\mathrm{n}}^2-4\mathrm{n}$$

Commented by I want to learn more last updated on 22/Oct/20

$$\mathrm{Thanks}\mathrm{sir}$$

Commented by 1549442205PVT last updated on 25/Oct/20

$$\mathrm{you}\mathrm{are}\mathrm{welcome}$$

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