Question

Va rog este urgent!
Dau corontita si inimioara!!:-)
Exercitiul 33 va rog!
Multesc anticipat!

Answer 1

se foloseste formula mediei aritmetice si anume 1+2+3+...+n=n(n+1)/2

rezolv pct. g) ca exemplu de aplicare:

5+6+7+...+81=(1+2+3+4+5+6+7+...+81)-(1+2+3+4)=(81x82)/2-(4x5)/2=
81x41-10=3311

Daca nu este clar astept un comentariu!

Answer 2

a)2+3+4+....+50= (50×51):2-1=2550:2-1=1275-1=
=1274

b)1+2+3+...+500=500×501:2= 250500:2=
=125250

c)1+97+2+999+3+198= (1+999)+(2+198)+(97+3)=
=1000+200+100=1300

d)1+2+3+...+124=124×125:2=15500:2=
=7750

e)2+4+6+...+600= (2×1)+(2×2)+(2×3)+...+(2×300)= 2×(1+2+3+4+5+...+300)=
=2×[(300×301)÷2]=2×(90300÷2)=90300(taie-i pe ambii 2, se anuleaza)

f)15+16+17+...+70=(70×71)÷2-14=4970:2=2485-14=2471

g)5+6+7+...+81=(81×82):2-4=6642:2-4=3321-4=
=3317

h)1+2+3+...+512=(512×513)÷2=262656:2=131328

i)317+318+...+400=(400×401):2=160400:2=
=80200

UF! Dar mult mai e! Coroana?!