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Rezolva ecuatiile:
a) x+ (x+1)+(x+2)+.....+(x+11)=78

b) 10+20+30+...+x0 =360

c) x+11+22+33+....+77 =2x-187


Răspuns :

12x+(1+2+3+4+5+6+7+8+9+10+11)=12x+12+12+11+11+11=12x+24+33=12x+57

am grupat cifrele doua cate doua de la extramitati   12x+57=78, 12x=21, x=21/12=7/4
c)x+11+22+33+44+55+66+77=2x-187
x+3*88+44=2x-187

x+264+44=2x-187
x+308=2x-187
x=308-187=121