Question

Cat fac 2+4+6+8+. 10. +78=.

Answer 1

Răspuns:

Explicație pas cu pas:

2+4+6+8+10+.......+78 =

= 2×1+2×2+2×3+2×4+2×5+.......+2×39 =

= 2×(1+2+3+4+5+.....+39) =

= 2×39×(1+39) : 2 =

= 39×40 =

= 1 560