Question

2+4+6+...+78
helppp repede e

Answer 1

2+4+6+...+78 =
= 2×(1+2+3+...+39) =
= 2 × 39 × (39+1) : 2=
= 2 × 39 × 40 : 2 =
= 78 × 20 =
= 1 560