a=1+2+3+.........+100

Răspuns :

1+ 2+ 3+........+100
100+99+98+....+1
100+1=101
101×100=10100
10100÷2=5050(a)
   
[tex]\displaystyle\\ A=1+2+3+.........+100= \frac{100(100+1)}{2}= 50\times 101 = \boxed{\bf 5050} [/tex]