sn=(x-1)+(x^2-3)+(x^3-5)+...+[x^n-(2n-1)]

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sn=(x-1)+(x^2-3)+(x^3-5)+...+[x^n-(2n-1)]sn=(x-1)+(x^2-3)+(x^3-5)+...+[x^n-(2n-1)]sn=(x-1)+(x^2-3)+(

sn=(x-1)+(x^2-3)+(x^3-5)+...+[x^n-(2n-1)]
sn=(x-1)+(x^2-3)+(x^3-5)+...+[x^n-(2n-1)]

sn=(x-1)+(x^2-3)+(x^3-5)+...+[x^n-(2n-1)]
sn=(x-1)+(x^2-3)+(x^3-5)+...+[x^n-(2n-1)]
=x+x^2+x^3+.+x^n+1+3+5+.+2n-1
=x(1-x^n)/(1-x)+(1+2n-1)*n/2
=x(1-x^n)/(1-x)+n^2