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# Use the formula S​ = n2 to find the sum of 1​ + 3​ + 5​ + ...​ +

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Use the formula S​ = n2 to find the sum of 1​ + 3​ + 5​ + ...​ +

861 = . ​(Hint: To find​ n, add 1 to the last term and divide by​ 2.)

Sep 6, 2017

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Use the formula S​ = n2 to find the sum of

1​ + 3​ + 5​ + ...​ + 861 = ?

​(Hint: To find​ n, add 1 to the last term and divide by​ 2.)

$$\begin{array}{|rcll|} \hline n &=& \frac{861+1}{2} \\ &=& \frac{862}{2} \\ &=& 431 \\ \hline \end{array}$$

$$\begin{array}{rcll} sum &=& n^2 \\ &=& 431^2 \\ &=& 185761 \\ \end{array}$$

$$\begin{array}{rcll} 1\ + 3\ + 5\ + 7\ + \ ... \ + 859\ + 861 &=& 185761 \\ \end{array}$$

Sep 6, 2017
edited by heureka  Sep 6, 2017