Question

Salut ! Ma puteti ajuta exercitiul este asa :
1+3+5+.......+99=
Daxa stiti ajutatima VA ROG MULT !!!!

Answer 1

=(1+99)×50:2=100×25=2500

Answer 2

$\displaystyle 1+3+5+...+99 \\ \\ 99=1+(n-1) \times 2 \\ \\ 99=1+2n-2 \\ \\ 2n=99-1+2 \\ \\ 2n=100 \\ \\ n= \frac{100}{2} \\ \\ n=50$

$\displaystyle S_{50}= \frac{2+49 \times 2}{2} \times 50 \\ \\ S_{50}= \frac{2+98}{2} \times 50 \\ \\ S_{50}= \frac{100}{2} \times 50 \\ \\ S_{50}=50 \times 50 \\ \\ S_{50}=2500$