"D 2019 plus 2 ori deschide paranteză 1 plus 2 plus 3 plus puncte puncte puncte plus 2018"
d) 2019 + 2·(1+2+3+ ... +2018)
[tex]\it 2019+2\cdot(1+2+3+\ ,,,\ +2018)=2019+2\cdot\dfrac{2018\cdot2019}{2}=\\ \\ \\ =2019+2018\cdot2019=2019\cdot(1+2018)=2019\cdot2019=2019^2[/tex]
c) 1+3+5+ ... +(2n-1) =n^2
1+3+5+ ... +49 = 25²
