Răspuns :
5k + 5(k + 1) + 5(k + 2) + 5(k + 3) + 5(k + 4) + 5(k + 5) = 165
5 * 6k + 5(1 + 2 + 3 + 4 + 5) = 165
30k + 5 * 15 = 165
30k = 165 - 75
30k = 90
k = 90 : 30
k = 3
5 * 3 = 15
5 * 4 = 20
5 * 5 = 25
5 * 6 = 30
5 * 7 = 35
5 * 8 = 40
15 + 20 + 25 + 30 + 35 + 40 = 165
5 * 6k + 5(1 + 2 + 3 + 4 + 5) = 165
30k + 5 * 15 = 165
30k = 165 - 75
30k = 90
k = 90 : 30
k = 3
5 * 3 = 15
5 * 4 = 20
5 * 5 = 25
5 * 6 = 30
5 * 7 = 35
5 * 8 = 40
15 + 20 + 25 + 30 + 35 + 40 = 165
5k+5[k+1]+5[k+2]+5[k+3]+5[k+4]+5[k+5]=165
⇒5k+5k+5+5k+10+5k+15+5k+20+5k+25=165
⇒30k+75=165
⇒30k=165-75
⇒30k=90⇒k=3;
⇒5·3=15;
⇒5·4=20;
⇒5·5=25;
⇒5·6=30;
⇒5·7=35
⇒5·8=40;
⇒15,20,25,30,35 si 40 sunt 6 multipli consecutivi ai lui 5 ,care respecta cerinta;
⇒5k+5k+5+5k+10+5k+15+5k+20+5k+25=165
⇒30k+75=165
⇒30k=165-75
⇒30k=90⇒k=3;
⇒5·3=15;
⇒5·4=20;
⇒5·5=25;
⇒5·6=30;
⇒5·7=35
⇒5·8=40;
⇒15,20,25,30,35 si 40 sunt 6 multipli consecutivi ai lui 5 ,care respecta cerinta;