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2014-10-09T10:53:51+03:00
1.
a) 4+8+12+.........+1996=4+(4+4*1)+(4+4*2)+...+(4+4*498)=4*498+4*(1+2+..+498)=4*498+4*498*499:2=1992+497004=498996
b) 7+14+21+.......+3157=7+(7+7*1)+...+(7+7*450)=7*450+7(1+2+3+...450)=7*450+7*450*451:2=3150+710325=713475
2.a) a=14 
b+c=25 
a+(b+c)=14+25=39
_---------------------------------
B)a=14
b+c = 25
a+3xb+3xc=a+3X(
b+c)=14+3x25=89
si la a la fel
dar multumesc orcum
nu este asa cum am scrias caa am si eu asa ceva tema
da dar aceste exerciti sunt de clasa 5 a
da
2014-10-09T13:01:27+03:00
1. a) 4(1+2+3+....+499)=4*499*500/2=2*499*500=499.000
 S-a folosit formula : 1+2+.....n=n(n+1)/2  (suma lui Gauss)
b) 7(1+2+....+451)=7*451*452/2=7*451*226=713.482
2. a) a +b +c= a + ( b + c )=14+25=39
    b) a+3*b+3*c=a + 3 * (b+c)=14+3*25=14+75=89