Arithmetic Series?

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1 Answer
Jul 17, 2018

#25#

Explanation:

#•color(white)(x)sum_(r=1)^nr=1/2n(n+1)#

#•color(white)(x)sum_(r=1)^n1=n#

#sum_(n=1)^5(2n-1)=2xx1/2n(n+1)-n#

#color(white)(xxxxxxxxx)=n(n+1)-n#

#color(white)(xxxxxxxxx)=n^2+n-n=n^2#

#sum_(n=1)^5(2n-1)=5^2=25#