Question

S=1+2+3+.................+20 si S=15+16+17+..............+70

Answer 1

S=1+2+3+...+20

S=20*(20+1)/2 formula lui Gauss

S=10*21

S=210

S=15+16+...+70

S=1+2+3+...+70 - (1+2+3+...+14)

S=70*71/2 -14*15/2

S=(4970 - 210)/2

S=4760/2

S=2380