Question

11 + 22+33+...+99=
111+222+...+999=
3+6+9+..+9a=
2X x1326=2652
repede va rog!

Answer 1

11 + 22+33+...+99=
=11(1+2+3+...+9)=
=11*9*(9+1)/2=
=11*9*5=
=495

111+222+...+999=
111(1++2+...+9)==
=111*9*(9+1)/2=
=111*9*5=4995

3+6+9+..+9a=
=3(1+2+3+...3a)=
=3*3a(3a+1)/2=
=9a(3a+1)/2
=13,5a²+4,5a

2X x1326=2652
x=2652:(1326*2)
x=1