Question

ex 15 la punctul C si D. VA ROGGGGG

Answer 1

formula e asa :
n+(n+k)+(n+2k)+(n+3k)+...+(n+mk)=cate numere sunt*(ultimul +primul):2
=> cate numere sunt=(ultimul- primul): din cat in cat merge +1
Deci 
n+(n+k)+(n+2k)+(n+3k)+...+(n+mk)={[(n+mk)-n]:k+1} * [(n+mk)+n]:2

c)1+3+5+...+99=[(99-1):2+1]*(99+1):2=50*100:2=2500
d) 3+7+11+15+...+43=[(43-3):4+1]*(43+3):2=11*46:2=253