Question

VA ROG FRUMOS DAU COROANA Ex 4​

Answer 1

Răspuns:

$1+3+5+7+...+101=?$

$a1=1,r=2$

$an=a1+(n-1)*r <=>101=1+(n-1)*2=>100=(n-1)*2$

$n-2=50=>n=51$

$S_{51}=\frac{51}{2}*(101+1)=\frac{51}{2} *102=> S= 51*51=51^2=2601$