Question

Calculati :
80+82+84+86+....+264=...
7+16+25+34+....862=
37+43+49+55+....+103=

Answer 1

80+82+...264=(80+264)x185:2=31820
suma are a264-79=185 de termeni
7+16+...862=(7+862)x96:2=41712
suma are 96 de termeni deoarece
7=9x0+7
16=9x1+7
25=9x2+7
....
862=9x95+7
si de la 0 la 95 avem 96 de numere
37+43+...+103=(37+103)x12:2=840
suma are 12 termeni deoarece
37=6x6+1
....
102=6x17+1
si 17-5=12

Answer 2

80=80+0x1
82=80+1x2
84=80+2x2
86=80+3x2
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264=80+263x2
a.80+82+84+86+...+264=696
b.7+16+25+34+...+862=7812
c.37+43+55+...+103=894
la fiecare am facut asa cum am facut la primul ex.
la b. am facut 
7=7+0x9
16=7+1x9
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862=7+861x9
si asa la fel la c. 
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103=37+102x6
ai inteles?
sper ca te-am ajutat