Question

2+4+6+...+30-1-3-5-....-29

Answer 1

aflam suma lui gauss pentru numerele pare

S1=2+4+6+...+30

S1=30+28+26+...+2

2S1=32+32+32+...+32

2S1=32*[(30-2):2+1]

2S1=32*15

2S1=480

S1=480:2

S1=240

AFLAM SUMA LUI GAUSS PENTRU NUMERELE IMPARE

S2=1+3+5+...+29

S2=29+27+25+...+1

2S2=30+30+30+...+30

2S2=30*[(29-1):2+1]

2S2=30*15

2S2=450

S2=450:2

S2=225

S1-S2=240-225=15