Question

a) 7+9+11+...+2013-5-7-9-...2011
b) 11+12+13+...+78
c) 5+10+15...+95
Repede va rog!!!!!!!

Answer 1

b) 11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30+31+32+33+34+35+36+37+38+39+40+41+42+43+44+45+46+47+48+49+50+51+52+53+54+55+56+57+58+59+60+61+62+63+64+65+66+67+68+69+70+71+72+73+74+75+76+77+78=3026

c) 5+10+15+20+25+30+35+40+45+50+55+60+65+70+75+80+85+90+95=1940

Answer 2

a) 7+9+11+...+2013-5-7-9-...-2011=
se reduc 7 cu -7, 9 cu -9 ......20011 cu -2011
=-5+2013
=2008
b) S=11+12+13+...+78
S=78+77+76+...+11
_________________
2×S=89+89+89+...+89
(78-11):1+1=67:1+1=67+1=68 termeni
2×S=89×68
S=89×68:2
S=89×34
S=3026
c)5+10+15+...+95=
=5×(1+2+3+...+19)
=5×19×(19+1):2
=5×19×20:2
=5×19×10
=50×19
=950